CBQE-2297: upr-rebalance imporve node stop/start

if a test asserts or doesn't finish keep track of
nodes that were stopped so that they can be started later.

Change-Id: Ib5a1785fd4eb81a5e84b927afc193f657ae4dbb0
Reviewed-on: http://review.couchbase.org/39172
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: Tommie McAfee <tommie@couchbase.com>