fix SSL handshake issue

The problem is that if any request library (for instance, `xmlrpclib`) gets imported earlier than `gevent.monkey.patch_socket` is called, then any https request fails during SSL handshake.

References:
* https://github.com/kennethreitz/requests/issues/1480#issuecomment-22604424
* https://github.com/swiftstack/ssbench/issues/69#issuecomment-17556190