Bug: Catch any underlying exceptions from http.HTTPException

Resolves https://github.com/GoogleCloudPlatform/google-auth-library-
         python-httplib2/issues/6

Author: Poogles

google_auth_httplib2.py

@@ -22,6 +22,11 @@
 from google.auth import transport
 import httplib2
 
+# httplib became http.client in 3.x
+try:
+    from http.client import HTTPException
+except ImportError:
+    from httplib import HTTPException
 
 _LOGGER = logging.getLogger(__name__)
 # Properties present in file-like streams / buffers.
@@ -115,7 +120,9 @@ def __call__(self, url, method='GET', body=None, headers=None,
             response, data = self.http.request(
                 url, method=method, body=body, headers=headers, **kwargs)
             return _Response(response, data)
-        except httplib2.HttpLib2Error as exc:
+        # TODO: httplib2 should catch the lower http error, this is a bug and
+        # needs to be fixed there.  Catch the error for the meanwhile.
+        except (httplib2.HttpLib2Error, HTTPException) as exc:
             raise exceptions.TransportError(exc)