Emit metrics for CAS

Patch by Sankalp Kohli, reviewed by brandonwilliams for CASSANDRA-7341
Merge branch 'cassandra-2.0' into cassandra-2.1
Emit metrics for CAS

Patch by Sankalp Kohli, reviewed by brandonwilliams for CASSANDRA-7341
Emit metrics for CAS

Patch by Sankalp Kohli, reviewed by brandonwilliams for CASSANDRA-7341
Merge branch 'cassandra-2.0' into cassandra-2.1