Add the couchbase repo to the perfrunner manifest

Change-Id: Ie0879a8cf65b75a8b6703636d47decfbfd275b19
Reviewed-on: http://review.couchbase.org/43212
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>