Notify placement changes on nova channel

Placement project is under nova governance now so
let's notify nova channel for placement repo changes
too.

Change-Id: Icc84cdf961f4a7b3d16bd09abf98714e492446c2

gerritbot/channels.yaml

@@ -1024,6 +1024,8 @@ openstack-nova:
     - openstack/os-resource-classes
     - openstack/os-traits
     - openstack/os-vif
+    - openstack/osc-placement
+    - openstack/placement
     - openstack/python-novaclient
   branches:
     - master