Added power_cycle_nodes script

Simple script that takes a project name and calls the CLI command to power cycle all of its nodes.

This PR was inteded to address the Trello backlog task ```trivial head node script to talk to HaaS API, power cycle machines...```, although now that I read it again I'm not sure that I actually addressed it.  Were we looking for something to actually run *on* the headnode?

I had to do some funky stuff to use the CLI module to do this.  Although, I don't know if there is a better option.
Quoting Ryan Abouzahra (2014-10-27 23:46:42)
>    What is the difference...?

According to the docs,

* `cStringIO` is much more performant.
* `StringIO` more completely implements the file-like interface (which I
  guess just means it emulates more of the methods provided by the file
  class?)

I think for our purposes, cStringIO's semantics are probably fine in all
cases; I don't think we really use anything other than `read()`.