Provide the right user to the _set_bugzilla_owner function

We were giving the user currently performing the action rather than the new point of
contact of the package.
If something happens, rollback

This prevent orphaning a package on pkgdb while some settings (FAS) are missing.
Fix the unit-tests to query the right database using the appropriate session

This explains why I was getting local data rather than the one generated for the tests.
Split the extras tests into two function so that the cache gets re-initialized in between