(Deferred) Mininet patches from Big Switch

So, here is the first batch of mininet patches from big switch; normally they would create the pull request, but to get things started and to facilitate some discussion and code review, I've created the pull request myself.

*This is (as far as I can tell) revised to have the correct rebase, though it seems to include my commits from the userovs branch on yuba. I'd suggest **discussing (only) the big switch changes here**, and discussing the userovs changes at: https://github.com/mininet/mininet/pull/4.*

I haven't reviewed everything, but a couple of things I've seen so far look pretty reasonable, including using sudo so Mininet is only root for the root-like things it needs to do (and so it can be imported into average python code not running as root), and a fix for the annoying control-c-kills-your-xterms (and other subprocesses) bug (assuming that the fix is good and works.)

Although this is a mass of patches, we may want to cherry-pick specific commits.

I'm (hopefully) cc'ing Ed and Mike from big switch so they can join the discussion.

/cc @eswierk @mscohen02 
/cc @jvimal @nikhilh