Stop running devstack-plugin-ceph-tempest on master
Stop running devstack-plugin-ceph-tempest on master

devstack-plugin-ceph-tempest is py2 job and not supposed
to run on master gate. devstack-plugin-ceph master gate already
run its py3 version devstack-plugin-ceph-tempest-py3.

We need to keep the devstack-plugin-ceph-tempest definition
for stable branches gate.

Change-Id: I6c512b29a0346db1f92de34b1dbfb56958fa2cad

openstack/devstack-plugin-ceph