Add the couchbase python client to the perfrunner manifest

Change-Id: I6764c3c37521f59966be7da1b072d1e537114a87
Reviewed-on: http://review.couchbase.org/43211
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>