'Send a HTTP HEAD request using keystone service catalog and auth
:param str url: the relative url to send the post request to
:param dict headers: The headers to use for the request
:param bool extra_headers: Boolean value than indicates if the headers
returned by the get_headers() method are to
be used but additional headers are needed in
the request pass them in as a dict.
:return: a tuple with the first entry containing the response headers
and the second the response body
:rtype: tuple'

def head(self, url, headers=None, extra_headers=False):

    return self.request('HEAD', url, extra_headers, headers)
