Disable quantum full runs on stable/grizzly

This commit disables quantum full tempest runs for commits
to stable/grizzly. The quantum full runs do not work in
stable/grizzly tempest so there is no point in running them
for backports.

Change-Id: Id9617640746fdb26bb630127fe86070df4adc4e9
Reviewed-on: https://review.openstack.org/26142
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Giampaolo Lauria <lauria@us.ibm.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins