Move gate-tempest-devstack-vm-large-ops to silent

Now that the  gate-tempest-devstack-vm-large-ops is working lets move it
to silent to see if it is stable enough to consider for gating.

This can be monitored using graphite.openstack.org to track the results.

Change-Id: Ice756312cf589ac6803b6ea0fafb51a99615adff
Merge "Move gate-tempest-devstack-vm-large-ops to silent"