Test modified to reschedule itself based on a flag setting. Without the
change in the parent commit, this test executes the callback indefinitely
and hangs but with the change it runs only once each time
mp_handle_pending() is called.
Modified-by: Angus Gratton <angus@redyak.com.au>
Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>