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

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.
The changes to this test stops the test suite from printing 'Purging database collections...' during a test run. I figured while I was in the area I would fix that.