CBQE-0: adding debug info for rebalance progress tests

Change-Id: Iaf4f22a2fcdac180e5466bc78442500042b81a1a
Reviewed-on: http://review.couchbase.org/26857
Reviewed-by: Deepkaran Salooja <deepkaran.salooja@globallogic.com>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>