MB-100: added scripts/analyze-rebalance-waiting.rb

Change-Id: Ic03657aee191811aa8bafbdc29dca6f71cc0fe31
Reviewed-on: http://review.couchbase.org/25745
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>