Cover the scenario fixed in "service: clean stale pidfile after
unclean daemon exit": a daemon with a pid:!/path config dies via
SIGKILL, leaving its pidfile behind, and the next instance must
still come up.
Add a 'serv -x' flag (refuse to start when the pidfile already
exists, dbus-style) so the test actually exercises the cleanup --
without it, plain 'serv' would happily overwrite the file and the
test would pass with or without the fix.
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
