MB-10759: print UI logs if rebalance operation failed

helps to find the problem when:
InvalidArgumentException: controller/rebalance failed when invoked with parameters:

Change-Id: Ib898ae0fb115ca69d77a706ccd88bd2872baff42
Reviewed-on: http://review.couchbase.org/35266
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: buildbot <build@couchbase.com>