Added arg and if statement prevents db_sync from being run where db service is not active i.e. the compute
Adds service to enable message bus for redhat

This is a requirement for getting libvirtd working.
Merge pull request #252 from bodepd/messagebus_libvirt

Adds service to enable message bus for redhat
Merge pull request #227 from aimonb/db_sync_fix

Adds check to ensure db_sync can be overridden.