AMI-545 proxy error handling

PLEASEREVIEW @donemiliano @edsplunk 

In some cases, res.json would still crash, as res.json sends http headers that specify content type.  If this is the case, the request is already pretty fucked, so just log the error and try not to die.
My only question would be, dow we have a test for this ? 
Just wondering if there is some coverage for this than can verify it