Couple of Netty fixes
a. Fix the port number by reading it from the bound channel
b. Fix the shutdown sequence to make sure we actually block on the channel
c. Fix the unit test to use two JVMs.
Flush serializer to fix zero-size kryo blocks bug.
Also convert the local-cluster test case to check for non-zero block sizes
Also flush serializer in revertPartialWrites
Merge branch 'master' of git://github.com/mesos/spark

Conflicts:
	core/src/test/scala/spark/ShuffleSuite.scala
Merge pull request #627 from shivaram/master

Netty and shuffle  bug fixes