In JSON mode, if not output is specified, write to stdout

Change-Id: If51c2263396369e2258575aa050b25e6355a1dc2
Reviewed-on: https://gerrit.instructure.com/46064
Reviewed-by: Michael Ziwisky <mziwisky@instructure.com>
Product-Review: Michael Ziwisky <mziwisky@instructure.com>
QA-Review: Michael Ziwisky <mziwisky@instructure.com>
Tested-by: Michael Ziwisky <mziwisky@instructure.com>