cephfs devstack plugin should not try to use tempest pin

[Tom Barron]

We removed the tempest pin from manila proper [1] but the ceph devstack plugin still expects to use it in pre_test_hook.sh [2] [3].

We should update the ceph devstack plugin to no longer expect a tempest pin.

[1] https://review.openstack.org/#q,Ia402fb79e1de5c9925f575d635b9928475095f86,n,z

[2] http://git.openstack.org/cgit/openstack/devstack-plugin-ceph/tree/manila/pre_test_hook.sh#n69

[3] http://logs.openstack.org/39/476239/12/check/gate-manila-tempest-minimal-dsvm-cephfs-nfs-centos-7-nv/4975d58/logs/devstack-gate-pre_test_hook.txt.gz#_2017-08-14_17_28_51_154

[Tom Barron (tpb)]

https://review.openstack.org/#/c/495386/ fixed this one