Enable merge commits for swift-milestone members.

The openstack/swift (and potentially openstack/python-swiftclient)
projects will be making use of feature branches, so grant the
swift-milestone group permission to upload merge commits for review.

Also make gerritbot report changes for feature/ec on the same
channels as swift master.

Change-Id: I3c86caf3715428f18fa0ee36f1cbc01f0627e188
Reviewed-on: https://review.openstack.org/36526
Reviewed-by: Khai Do <zaro0508@gmail.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: John Dickinson <me@not.mn>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins