MB-11325: print_UI_logs if rebalance stuck in RebalanceTask

Change-Id: I0c518cbb00e46d2c6c49ff1f5a1de9e6dac11140
Reviewed-on: http://review.couchbase.org/37900
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Meenakshi Goel <meenakshi.goel@globallogic.com>