establish the email connection closer to the send (bug 951703)

https://bugzilla.mozilla.org/show_bug.cgi?id=951703

This _hopefully_ fixes the connection timeout error from [mat's gist](https://gist.github.com/diox/502a20a58d156e5d375a).

There are no tests for `send_mail` in `apps/amo/tests/test_amo_utils.py` so hopefully this doesn't break anything. The only reference to connection was in `send` so I don't see why we can't move that line to right before it is used.