fsmonitor: add timeout to daemon stop command

fsmonitor: add timeout to daemon stop command

The "fsmonitor--daemon stop" command polls in a loop waiting for the
daemon to exit after sending a "quit" command over IPC.  If the daemon
fails to shut down (e.g. it is stuck or wedged), this loop spins
forever.

Add a 30-second timeout so the stop command returns an error instead
of blocking indefinitely.

Signed-off-by: Paul Tarjan <github@paulisageek.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>