SLES 15 fails acceptance tests due to not providing an os.release.minor value

For SLES 15, we now parse /etc/os-release instead of Suse's old /etc/SuSE-release file to determine os facts. Since SLES 15 doesn't have any point-releases yet, the VERSION_ID value it's parsing from /etc/os-release is simply "15". This is resulting in there being no os.release.minor to return.

The acceptance test os_processors_and_kernel.rb uses a regex that expects os.release.full to return something with a point release - so "15.0" would pass, but "15" would not.

After some discussion in the Platform Core channel, the consensus was that os.release.minor should always return a value, given that there's likely code which relies upon it to perform things like version arithmetic or comparisons.