Reduce totalBlockFor() for LOCAL_* consistency levels

patch by Nicolas Douillet; reviewed by Aleksey Yeschenko for
CASSANDRA-8058
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/service/DatacenterWriteResponseHandler.java
Merge branch 'cassandra-2.1' into trunk
Merge remote-tracking branch 'origin/trunk' into 7692-3.0