Cluster Support Prototype

This is the beginning of providing some basic cluster support in Mininet proper. It is currently implemented as a few scripts in examples/ as well as a utility script to help with setting up the authentication via ssh. It's certainly a work in progress and has many limitations, but the ultimate goal is to provide seamless operation over a cluster with minimal changes to the Mininet API, CLI, and command line usage.

This call fails when the dstNode is not in it's own namespace. (There was an error that was suppressed before the performance enhancements pull request was merged.)

What is the purpose of srcNode? It never seems to be used.