Simplify tests that can time out

Simplify tests that can time out

There are basically two patterns:

* something should stop the main loop within n seconds; if not, that's
  failure (this is now loop_run_with_timeout)
* run the main loop for n seconds, then check whether things we wanted
  to happen happened (this is now loop_run_with_non_fatal_timeout)

The latter is basically a bug in itself; I'm not going to fix that
right now, but I did mark it as deprecated.

In both cases, we want to adjust the timeout for running under Valgrind
or Callgrind, which makes everything slow.