SPARK-1189: Add Security to Spark - Akka, Http, ConnectionManager, UI use servlets

resubmit pull request.  was https://github.com/apache/incubator-spark/pull/332.
This is what the unique connectionId is for. If the message returned has the connectionId from when it sent the security message and is in the connectionsawaitingsasl queue then its a response, otherwise the connectionId wouldn't match. 

In this case Alice sends a message to Bob. 
  - connectionAwaitingSasl on Alice gets Alice_1 added and Alice_1 is connecitonId of that message
Bob sends message to Alice
  - connetionAwaitingSasl on Bob gets Bob_1 added and Bob_1 is connectionId of that message.
Bob gets Alices first message, checks the connectionId in that message which is Alice_1 and it isn't in the connectionsAwaitingSasl because it only contains Bob_1 so acts as the server.