On master, drop Ubuntu 16.04 "Xenial" LTS and Debian 9 "stretch"

[stephengtuggy]

Thank you for submitting a pull request and becoming a contributor to the Vega Strike Core Engine.

Please answer the following:

Code Changes:

• Have the PR Validation Tests been run? See https://github.com/vegastrike/Vega-Strike-Engine-Source/wiki/Pull-Request-Validation
• This is a documentation change only
• This is a CI/CD/build system change only

Issues:

• Closes On master, drop support for Ubuntu 16.04 "xenial" and Debian 9 "stretch" #528
• Closes script/bootstrap: Update openSUSE version detection logic to match what's on build-system-docker-images #529

Purpose:

• What is this pull request trying to do? Drop support for Xenial and stretch on master, to pave the way for CMake v3.11 and gtest unit tests
• What release is this for? 0.9.x/1.0.x
• Is there a project or milestone we should apply this to? 0.9.x/1.0.x

[stephengtuggy]

Should I drop Xenial and stretch from the build scripts and from CMakeLists.txt in the same PR? I suppose I should.

[stephengtuggy]

Thanks, @nabaco . Unfortunately, I had added 4 more commits on my local machine last night, and another one this morning. Hopefully it's not too much trouble to review those too?

[BenjamenMeyer]

I'd prefer we change the scripts back to using /bin/bash instead of using /usr/bin/env bash; but I'm not going to block. See my comment on the one case for more info/discussion.

[BenjamenMeyer]

/bin/bash is actually guaranteed to be there per Linux Standard Base.
/usr/bin/env is not.

There's various arguments either way for most things, and most scripts engines it can make sense. However, /bin/bash and /bin/sh are two that have to be around for a basic system to function and can be directly relied upon so they don't make sense to export out to /usr/bin/env.

$0.02

[stephengtuggy]

Hmm. I can look this up later, I suppose. Anyway, thanks for approving the PR