[SPARK-5444][Network]Add a retry to deal with the conflict port in netty server.

If the `spark.blockMnager.port` had conflicted with a specific port, Spark will throw an exception and exit.
So add a retry to avoid this situation.

Author: huangzhaowei <carlmartinmax@gmail.com>

Closes #4240 from SaintBacchus/NettyPortConflict and squashes the following commits:

cc926d2 [huangzhaowei] Add a retry to deal with the conflict port in netty server.