Add logging to #openstack-gate

To facilitate discussion around coordinating fixes for bugs in
various projects participating in integration testing, a new
channel was created: #openstack-gate. This change requests that
it is permanently logged using eavesdrop.

Change-Id: I72ccfb96cda129c851bd3b0eed1e0b940ca04a82
Merge "Add logging to #openstack-gate"