fixes #6992 - ensure rhel 5 repos can be used by el5 clients

We can not publish the repos prior to syncing as this will cause
pulp to set the checksum on the repos to sha256.  See https://bugzilla.redhat.com/show_bug.cgi?id=1127793
We also need to pull the checksum after sync and add it to the repo
to ensure that clones use the same checksum
Merge pull request #4551 from jlsherrill/6992

fixes #6992 - ensure rhel 5 repos can be used by el5 clients