tests: skip RepoTest.test_const_install.

activate_sack() fails under the Koji environment as /run/user is not writable
for the metadata lock.
New version: 0.4.2
build: 0.4.2-1
tests: cleanups in support.py
tests: reenable the repo cost testing again.

This takes some refactoring and hawkey needed to improve support for
loading real Yum MD into the testing sacks (see hawkey commit d9d7184).
Fix error handling in Base.downgrade and YumBaseCli.downgradePkgs.
Fix error handling in Base.update and YumBaseCli.updatePkgs.
Fix error handling in Base.remove and YumBaseCli.erasePkgs.
Fix error handling in Base.install and YumBaseCli.installPkgs.