Cherry pick from https://review.openstack.org/#/c/39115/,
Update references with new Mailing List location

Yesterday, openstack@lists.launchpad.org was migrated with
all users to openstack@list.openstack.org.

This patch updates references to the old mailing list with the
new, to ensure that people encountering them don't accidentally
try and join the old list!

Change-Id: I3a05cb23bca5e77575e42e9d3cef49dc33918e8f