fix config opts in objectstore.rgw
fix config opts in objectstore.rgw

The config opts of rgw_admin_credentials group are not mentioned
in ceilometer/opts.py, the non-existent ceilometer.objectstore.rgw.OPTS
should be ceilometer.objectstore.rgw.CREDENTIAL_OPTS

Change-Id: Ifb3ea440ab23ea80a45ed245d06cca4898635262
Closes-Bug: #1425554

fabian4/ceilometer,openstack/aodh,redhat-openstack/ceilometer,idegtiarov/ceilometer,openstack/ceilometer,pkilambi/ceilometer,sileht/aodh,fabian4/ceilometer,mathslinux/ceilometer,r-mibu/ceilometer,openstack/aodh,pczerkas/aodh,redhat-openstack/ceilometer,maestro-hybrid-cloud/ceilometer,cernops/ceilometer,cernops/ceilometer,pczerkas/aodh,eayunstack/ceilometer,pkilambi/ceilometer,sileht/aodh,isyippee/ceilometer,chungg/aodh,openstack/ceilometer,r-mibu/ceilometer,isyippee/ceilometer,mathslinux/ceilometer,maestro-hybrid-cloud/ceilometer,ityaptin/ceilometer,eayunstack/ceilometer,chungg/aodh,idegtiarov/ceilometer,ityaptin/ceilometer