event-collector queue: Keep connections open

Python requests sessions can take advantage of keep-alive, but you have to
read from the response.content for it to work.

http://docs.python-requests.org/en/latest/user/advanced/#keep-alive

r2/r2/lib/eventcollector.py

@@ -218,6 +218,9 @@ def _chunk_events(self, events):
     def publish(self, events):
         for some_events in self._chunk_events(events):
             resp = self._publish(some_events)
+            # read from resp.content, so that the connection can be re-used
+            # http://docs.python-requests.org/en/latest/user/advanced/#keep-alive
+            ignored = resp.content
             yield resp, some_events