Revert from urllib2 -> urllib

Rather than urllib2, we'll simply catch more exceptions. In this case, a
KeyError when looking at HipChat's JSON error response body.

Auditors: csilvers

Test Plan:

  $ python -c 'import deploy_pipeline; deploy_pipeline._email_to_hipchat_name("chris@khanacademy.org")'
  WARNING:root:Fetching email->hipchat mapping failed; will guess.  (KeyError: 'users')