Don't post merges in openstack-dev and openstack-nova

Merged patches are almost never relavent for any sort of conversation,
the work is already done, so no reason to post it.

Disable these for two of the bigger rooms, openstack-dev and
openstack-nova.

Change-Id: Ib7449c5dd4468057c98e4d755a6b96d2a1f9f244
Merge "Don't post merges in openstack-dev and openstack-nova"