editquality: set Content-type when sending events to EventGate
The error that we were debugging recently about EventGate
rejecting the test score event (from ml-staging) due to
the missing meta.stream value was due to the content type
set by Tornado, application/x-www-form-urlencoded, that
causes EventGate to probably fail parsing the POST's body
returning the error.
I tested an event generated by this code using the "wrong"
Content-Type and curl (from stat1004), I was able to
reproduce the error without any issue. Using the correct
Content-Type worked perfectly.