Fix unreliable image streaming

Return the request stream directly after pausing it, instead of setting up an
undocumented 'request' listener. Error handling didn't seem to work for
stream-based requests. This led to some image requests never finishing
whenever there was some issue, which in turn prevented the remainder of the
tasks from ever running.

Change-Id: Ic69863791ef4179de1d61295ec85cb76e5b13e16