Use constants so we won't have to edit a dozen places in the test when
the package versions are bumped.
(cherry picked from commit 6242ae8b18)
Related: rhbz#171282
the unittest suite is currently executed on Fedora where tmux is
version 2.8 but on RHEL 8 it is 2.7 and depsolve fails when
building images.
Related: rhbz#1653934