Clean up Cinder service checks

Use $CINDER_SERVICE_NAMES in all is_service_enabled calls where
one or more services are checked; i.e. replace 'cinder' as the argument
to eliminate the hack in the is_service_enabled() function.

TODO: remove the cinder test from is_service_enabled() after a transition period

Change-Id: I6079ba253517d5418f8d193a22d390851696b342
Merge branch 'info-update' into dt-test
Merge branch 'enabled-cinder' into dt-test
Merge branch 'enabled-glance' into dt-test
Merge branch 'plugin-functions' into dt-test
Merge branch 'samples-update' into dt-test
Merge branch 'cleaner' into dt-test