<oo-admin-check-sources.py> Bug 1026793, Added catch block to find_package_conflicts

https://bugzilla.redhat.com/show_bug.cgi?id=1026793

`YumBase` call in `OpenShiftCheckSources.packages_for_repo` raised an
uncaught `RepoError`. This condition was reachable on systems where a
broken repo config exists and `yum-plugin-priorities` is
installed. Added logic to catch the `RepoError` and bail out.