Use python-requests for RPC

`urllib2.urlopen` is bad at SSL, in particular, it does not perform any type of certificate verification. From https://docs.python.org/2/library/urllib2.html:

> Warning HTTPS requests do not do any verification of the server’s certificate.

This PR replaces `urllib2` with the more modern more humane `requests` library which uses `urllib3` that does SSL correctly.