Consult target when deciding to upgrade service
Consult target when deciding to upgrade service

The target side's enabled services should be queried when determining
whether or not to upgrade a service.  This allows sideways upgrades
that involve adding or removing services during the upgrade/migration.

Change-Id: I94569b35342d20fd5ef4d92d3f97cee6cfc42291

openstack-dev/grenade,openstack-dev/grenade,dtroyer/grenade,dtroyer/grenade