Disable EPEL repository when installing NGINX

[sbesson]

Recent patch releases of nginx show difference in the default configuration folder between NGINX and EPEL repositories
Since the previous task deal with the installation of the stable NGINX repository, this ensures this repository is used.

This is a similar issue to the one dealt with in ome/devspace#183. In the case of our Ansible playbooks, this was discovered in the context of a pilot IDR server with Nginx 1.20.1-2el7 always serving the default page. The content of /etc/nginx/nginx.conf shipped by the EPEL rpm now includes a default server section and no longer works out-of-the box with the nginx configuration created by https://github.com/ome/ansible-role-omero-web/blob/d6fa479790aa272f8ebca048dfaf3ba4cca4a07e/tasks/web-nginx.yml#L20-L26. This does not affect advanced playbooks e.g. using ome.nginx_proxy or manually overwriting nginx.conf

This PR makes the minimal change to ensure the existing playbooks keep working as expected.

Proposed tag: 2.1.2

[sbesson]

For reference, the following commands

yum install -y epel-release
yum install -y https://nginx.org/packages/centos/7/noarch/RPMS/nginx-release-centos-7-0.el7.ngx.noarch.rpm
yum install -y --disablerepo=epel nginx
cp /etc/nginx/nginx.conf /tmp/nginx-1.20.1-1.el7.conf
yum remove -y nginx
yum install -y nginx
diff /tmp/nginx-1.20.1-1.el7.conf /etc/nginx/nginx.conf

expose the diff in the NGINX configuration files

[root@b6ef96a3dc61 /]# diff /tmp/nginx-1.20.1-1.el7.conf /etc/nginx/nginx.conf
0a1,8
> # For more information on configuration, see:
> #   * Official English Documentation: http://nginx.org/en/docs/
> #   * Official Russian Documentation: http://nginx.org/ru/docs/
> 
> user nginx;
> worker_processes auto;
> error_log /var/log/nginx/error.log;
> pid /run/nginx.pid;
2,7c10,11
< user  nginx;
< worker_processes  auto;
< 
< error_log  /var/log/nginx/error.log notice;
< pid        /var/run/nginx.pid;
< 
---
> # Load dynamic modules. See /usr/share/doc/nginx/README.dynamic.
> include /usr/share/nginx/modules/*.conf;
10c14
<     worker_connections  1024;
---
>     worker_connections 1024;
13d16
< 
15,17d17
<     include       /etc/nginx/mime.types;
<     default_type  application/octet-stream;
< 
24,27c24,36
<     sendfile        on;
<     #tcp_nopush     on;
< 
<     keepalive_timeout  65;
---
>     sendfile            on;
>     tcp_nopush          on;
>     tcp_nodelay         on;
>     keepalive_timeout   65;
>     types_hash_max_size 4096;
> 
>     include             /etc/nginx/mime.types;
>     default_type        application/octet-stream;
> 
>     # Load modular configuration files from the /etc/nginx/conf.d directory.
>     # See http://nginx.org/en/docs/ngx_core_module.html#include
>     # for more information.
>     include /etc/nginx/conf.d/*.conf;
29c38,81
<     #gzip  on;
---
>     server {
>         listen       80;
>         listen       [::]:80;
>         server_name  _;
>         root         /usr/share/nginx/html;
> 
>         # Load configuration files for the default server block.
>         include /etc/nginx/default.d/*.conf;
> 
>         error_page 404 /404.html;
>         location = /404.html {
>         }
> 
>         error_page 500 502 503 504 /50x.html;
>         location = /50x.html {
>         }
>     }
> 
> # Settings for a TLS enabled server.
> #
> #    server {
> #        listen       443 ssl http2;
> #        listen       [::]:443 ssl http2;
> #        server_name  _;
> #        root         /usr/share/nginx/html;
> #
> #        ssl_certificate "/etc/pki/nginx/server.crt";
> #        ssl_certificate_key "/etc/pki/nginx/private/server.key";
> #        ssl_session_cache shared:SSL:1m;
> #        ssl_session_timeout  10m;
> #        ssl_ciphers HIGH:!aNULL:!MD5;
> #        ssl_prefer_server_ciphers on;
> #
> #        # Load configuration files for the default server block.
> #        include /etc/nginx/default.d/*.conf;
> #
> #        error_page 404 /404.html;
> #            location = /40x.html {
> #        }
> #
> #        error_page 500 502 503 504 /50x.html;
> #            location = /50x.html {
> #        }
> #    }
31d82
<     include /etc/nginx/conf.d/*.conf;
32a84
> 

[sbesson]

21eacd5 includes a new Molecule test for the issue fixed in this PR. Without the fixes, #12 and https://github.com/ome/ansible-role-nginx/pull/12/checks?check_run_id=2950556354 demonstrate it is failing

     =================================== FAILURES ===================================
    ______________ test_nginx_configuration[ansible://nginx-disabled] ______________
    
    host = <testinfra.host.Host object at 0x7f7cab8bf6a0>
    
        def test_nginx_configuration(host):
            c = host.file('/etc/nginx/nginx.conf')
            assert 'http {' in c.content_string
    >       assert 'server {' not in c.content_string
    E       assert 'server {' not in '# For more ...  }\n\n}\n\n'
    E         'server {' is contained here:
    E           onf;
    E           
    E               server {
    E                   listen       80;
    E                   listen       [::]:80;
    E                   server_name  _;
    E                   root         /usr/share/nginx/html;
    E           
    E                   # Load configuration files for the default server block.
    E                   include /etc/nginx/default.d/*.conf;
    E           
    E                   error_page 404 /404.html;
    E                   location = /404.html {
    E                   }
    E           
    E                   error_page 500 502 503 504 /50x.html;
    E                   location = /50x.html {
    E                   }
    E               }
    E           
    E           # Settings for a TLS enabled server.
    E           #
    E           #    server {
    E           #        listen       443 ssl http2;
    E           #        listen       [::]:443 ssl http2;
    E           #        server_name  _;
    E           #        root         /usr/share/nginx/html;
    E           #
    E           #        ssl_certificate "/etc/pki/nginx/server.crt";
    E           #        ssl_certificate_key "/etc/pki/nginx/private/server.key";
    E           #        ssl_session_cache shared:SSL:1m;
    E           #        ssl_session_timeout  10m;
    E           #        ssl_ciphers HIGH:!aNULL:!MD5;
    E           #        ssl_prefer_server_ciphers on;
    E           #
    E           #        # Load configuration files for the default server block.
    E           #        include /etc/nginx/default.d/*.conf;
    E           #
    E           #        error_page 404 /404.html;
    E           #            location = /40x.html {
    E           #        }
    E           #
    E           #        error_page 500 502 503 504 /50x.html;
    E           #            location = /50x.html {
    E           #        }
    E           #    }
    E           
    E           }
    
    tests/test_default.py:56: AssertionError
    =========================== short test summary info ============================
    FAILED tests/test_default.py::test_nginx_configuration[ansible://nginx-disabled]

With 4373dfd, an additional tasks checks whether EPEL is installed and disables it conditionally. The Molecule tests are now passing on this PR and IDR/deployment#337 tests the fix in a more advanced Ansible playbook context.

[sbesson]

Raised at OME standup this morning. No objection raised. Merging, releasing and updating the downstream playbooks