HBASE-12086 Fix bug of HTableMultipliexer

Signed-off-by: Elliott Clark <eclark@apache.org>

Conflicts:
	hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncProcess.java
	hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestHTableMultiplexer.java