1132663 - pulp-manage-db now has a --dry-run flag.

https://bugzilla.redhat.com/show_bug.cgi?id=1132663

This flag causes pulp-manage-db to returns 1 if changes
would have been made by pulp-manage-db and 0 if everything is up-to-date.
does `load_content_types()` need to be checked for --dry-run?