Cause gabbi to skip on no storage sooner
Cause gabbi to skip on no storage sooner

This avoids problems interacting with the global CONF used by
prepare_service that happen when the fixture is skipped. If we skip
before ever accessign the CONF we have a better known state.

This problem was discovered by comparing runs of the gabbi tests
with mongo and mysql (they only work with mongo, by design).

Change-Id: I9567fb0b37e68cd92f141697e4af8882c10a33f7

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