The variables are set to the git revision from which the build is
triggered and rpm version from the spec file, if it is build using RPM.
This can be later used to query exact source version while
running osbuild-composer.
It is necessary to use both, because none of them is available in all
possible scenarios.
Use either git-rev (preferably) or RPM version (NEVRA) instead of the
"devel" build type. It was just a placeholder.
