MySQL's date time's appear to have a 1 second threshold, so we need to make sure the queue items added for the tests are available as soon as they are added. Before this change, the available_after was set to `datetime.utcnow()`, and, if the `get` was called within 1 second, then its check would fail.
This change defaults the ordering requirement of queue items to be off
and only enables it for the build manager. This should make the queries
for getting queueitems significantly faster for every other use case.
