<oo-admin-check-sources.py> Bug 1023361, fix reference to unassigned var

This commit places more find_package_conflicts logic in the try: block
so that the ose_pkgs list never gets referenced if the repoid being
checked doesn't match an enabled repo.

This also adds a check to prevent the rhel6 base repo from being
checked if it's not in the enabled repoids list
Merge pull request #113 from dobbymoodge/check-sources

<oo-admin-check-sources.py> Bug 1023361, fix reference to unassigned var