CBQE-0: remove output_time param in rebalance tests

this param is never used and useless

Change-Id: I72862124caffcab5ed8d85a0a69f861b3cde2fd4
Reviewed-on: http://review.couchbase.org/36826
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>