Don't print rebalance progress tons of decimals

We don't need that accurate percentag ;)

INFO - rebalance percentage : 79.7526041667 %

reduced to:

INFO - rebalance percentage : 75.82 %

Change-Id: Ifb9786fbd4440ccdad4c5ac22fc25f1f5ab1a6af
Reviewed-on: http://review.couchbase.org/40689
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>