Summary:
This is a first step towards python3 compatibility. Specifically, it
tackles:

 - `cPickle`: uses six.moves
 - `Queue`: uses six.moves
 - `urllib2`: uses six.moves and changes `urllib2.urlopen` to `urllib.request.urlopen`

Also, fundamentally it changes the types of all config "byte" types to
"string" types. Those configurations aren't un-encoded byte streams but very
specifically ascii (or unicode encoded) strings which are specified and
consumed by human eyes.

Reviewed By: rbgirshick

Differential Revision: D9662024

fbshipit-source-id: b8372f685b57ec4260ae881a2f8bb7967f337b10