db_sync: correct logic, do not ignore failures

Simplify and correct logic to not ignore errors which may occur when
checking the db_version using the manage tools.

Also remove no longer needed exit_status module.
No, I specifically wanted it to either be True or False when coming from a service. Setting to True always syncs the DB (which we don't want by default) and to False never syncs the DB (which only neutron wanted). Seemed like this was the only logic option which didn't sync by default but allowed for overrides either way.