test: regression for stale pidfile cleanup after unclean exit

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>

test/Makefile.am

@@ -41,6 +41,7 @@ EXTRA_DIST		+= global-envs.sh
 EXTRA_DIST		+= initctl-status-subset.sh
 EXTRA_DIST		+= notify.sh
 EXTRA_DIST		+= pidfile.sh
+EXTRA_DIST		+= stale-pidfile.sh
 EXTRA_DIST		+= pre-post-serv.sh
 EXTRA_DIST		+= pre-fail.sh
 EXTRA_DIST		+= process-depends.sh
@@ -84,6 +85,7 @@ TESTS			+= global-envs.sh
 TESTS			+= initctl-status-subset.sh
 TESTS			+= notify.sh
 TESTS			+= pidfile.sh
+TESTS			+= stale-pidfile.sh
 TESTS			+= pre-post-serv.sh
 TESTS			+= pre-fail.sh
 TESTS			+= process-depends.sh