Use the proper time for the carbon pipeline.

Summary:
timestamps have to be UTC for carbon.  I added code to do that for the
pickle protocol.

We *could* do that for the carbon text protocol as well, but
   http://docs.hostedgraphite.com/#metric-data-format
explains how you can leave the timestamp out, so I do that to fit more
data into one packet.

Test Plan: tools/runtests.py event_log_test.py

Auditors: chris

Differential Revision: http://phabricator.khanacademy.org/D8181