Cleanup http connections and other unnecessary fields in DAG Deletion tracker classes.

1. LocalContainerLauncher
I'm confused why we go through the trouble of serializing the hardcoded value of zero into the aux service protocol buffer, stuff it into the env, then immediately go fetch it back out and extract the integer from the byte buffer. Isn't this a complicated way to say, shufflePort = 0?

2. tezDefaultComponentName only needs to be computed when cleanupDagDataOnComplete is true. Actually may not be needed at all, see related comment for DagDeleteRunnable below.

3. DagDeleteRunnable
tezDefaultComponentName is unused? I think this transitively means pluginName is unused in DeletionTracker which would simplify it's constructor signature.

4. DeletionTracker
Nit: addNodeShufflePorts method name being plural implies more than one port can be added but it's only for adding a single node, port pair.

5. AMContainerHelpers
As Sidd mentioned before, we should avoid the redundant conf key lookup when creating each container launch context.

6. DagDeleteRunnable
Do we need to do any cleanup on the httpConnection?

7. DeletionTrackerImpl
What if the submission to the executor throws RejectedExecutionException because the executor was already shutdown and a late dagComplete was invoked?