More comprehensive logs during mysql initialization

[aario]

More comprehensive logs during mysql initialization and also visible error messages.
The idea came when I faced a problem with initialization of magento:

mysql                      | 2018-02-28T09:41:21.166088090Z 2018-02-28T09:41:21.166046Z 0 [Note] mysqld: ready for connections.
mysql                      | 2018-02-28T09:41:21.166104229Z Version: '5.7.21'  socket: '/var/run/mysqld/mysqld.sock'  port: 0  MySQL Community Server (GPL)
mysql                      | 2018-02-28T09:41:21.921672269Z MySQL init process in progress...
mysql                      | 2018-02-28T09:41:22.932179525Z MySQL init process in progress...
.
.
.
mysql                      | 2018-02-28T09:41:51.203276913Z MySQL init process in progress...
mysql                      | 2018-02-28T09:41:52.206185839Z MySQL init process failed.

There were two solutions on the internet to remove MYSQL_HOST from environment variables and to remove memory limit for docker container both of which was not the case for me. I read through the init script to realize that it tries to send a simple select 1 to the mysql and if it fails it thinks the mysql is still initializing. So continues to retry. When I tried the same select command manually:

echo 'SELECT 1' | mysql --protocol-=socket -uroot -hlocalhost --socket=/var/run/mysqld/mysqld.sock
mysql: [ERROR] unknown variable 'character_set_client=utf8'

I just realized that it's an error with my config file. So far so good. But:
Isn't it better for the init script to show the actual error message of mysql when it is retrying?
This feature can save hours of frustration for developers. That is why I prepared this pull request.

[aario]

stderr can be very useful sometimes. We should not always suppress it. So here I removed the '&'.

[yosifkit]

Apologies for the very long tail 🙇‍♂️

It seems with #471, this was improved:

mysql/.template.Debian/docker-entrypoint.sh

Line 92 in d284e15

mysql_note "Waiting for server startup"

mysql/.template.Debian/docker-entrypoint.sh

Line 107 in d284e15

mysql_error "Unable to start server."