fix build on RHEL6,7 (proper cmake is cmake3)

[chipitsine]

No description provided.

[vbwagner]

Where do you get openssl 1.1 for RHEL7? I haven't bother to support ancient version of cmake in RHEL/CentOS/Oracle linux, because they don't include openssl 1.1 anyway.

[chipitsine]

RHEL7 is not ancient. it is still supported. surprize, it is the latest RHEL

we roll our own RPM with openssl-1.1.0

[vbwagner]

cmake3 is missing from RHEL distribution. One need to add EPEL repositories to be able to download it
But if one have EPEL, it is available for centos 6 releases as well. And your pull request doesn't support it. (and it is still siupported too).

[chipitsine]

what I'm going to do (in mid term) is to create Fedora COPR repo with supported builds.

I haven't decided yet whether to support RHEL6 or not (we do not use it, so I can leave it to people who really needs it, right?)

currently, we deploy engine on RHEL7, so I adopted build system to it. unfortunately, I cannot write in spec "it depends on EPEL, only certain packages like cmake3"

[chipitsine]

wait a moment. I'll do smoke test on CentOS 6

[chipitsine]

is it ok now?