replace httplib2 with requests to avoid SSL certificate validation error

Replace httplib2 with requests library (http://docs.python-requests.org/en/latest/) as httplib2 does not support the CA provided by backplane2.0.  By default, httplib2 only supports the following certs - http://code.google.com/p/httplib2/source/browse/python2/httplib2/cacerts.txt.