Enable akka cluster mode
support master HA
optimize the imports
HA
add master log
Merge branch 'master' of https://github.com/intel-hadoop/gearpump

Conflicts:
	src/main/scala/org/apache/gearpump/cluster/Worker.scala
	src/main/scala/org/apache/gearpump/cluster/main/Local.scala
	src/main/scala/org/apache/gearpump/cluster/main/Master.scala
	src/main/scala/org/apache/gearpump/cluster/main/Worker.scala