Add 'nodetool sethintedhandoffthrottlekb'

patch by lyubent; reviewed by slebresne for CASSANDRA-7635
Merge commit 'd1c4d50ee05cb6be19d60c2e58a19b0e1fb93023' into cassandra-2.1.0
Merge branch 'cassandra-2.1.0' into cassandra-2.1