daemon: tests: add a test for missed SIGTERM

This is somewhaht hard to test reliably, but we'll give it a shot.  Startup
a sleep(1) daemon with a hefty restart delay.  In refactoring of daemon(8),
we inadvertently started dropping SIGTERMs that came in while we were
waiting to restart the child, so we employ the strategy:

 - Pop the child sleep(1) first
 - Wait for sleep(1) to exit (pid file truncated)
 - Pop the daemon(8) with a SIGTERM
 - Wait for daemon(8) to exit

The pidfile is specifically truncated outside of the event loop so that we
don't have a kqueue to catch it in the current model.

PR:		277959
Reviewed by:	des, markj
Differential Revision:	https://reviews.freebsd.org/D47005

usr.sbin/daemon/tests/daemon_test.sh

@@ -154,6 +154,43 @@ restart_child_cleanup() {
 	[ -f daemon.pid ] && kill `cat daemon.pid`
 }
 
+atf_test_case restart_hang cleanup
+restart_hang_head() {
+	atf_set "descr" "daemon should terminate with SIGTERM even pending child restart"
+}
+restart_hang_body() {
+	daemon -rP daemon.pid -R 10 -p sleep.pid sleep 300
+	atf_check -s exit:0 test -f daemon.pid
+	atf_check -s exit:0 test -f sleep.pid
+	read sleep_pid < sleep.pid
+	1>&2 echo "$sleep_pid"
+	kill "$sleep_pid"
+
+	# Wait up to 5s for the child to exit
+	for t in `seq 0 0.1 5`; do
+		[ ! -s "sleep.pid" ] && break
+		sleep 0.1
+	done
+
+	atf_check test ! -s "sleep.pid"
+
+	read daemon_pid < daemon.pid
+	kill -TERM "$daemon_pid"
+
+	# Wait up to 10s for the daemon to terminate
+	for t in `seq 0 0.1 10`; do
+		[ ! -f "daemon.pid" ] && break
+		sleep 0.1
+	done
+
+	atf_check test ! -f "daemon.pid"
+	atf_check test ! -f "sleep.pid"
+}
+restart_hang_cleanup() {
+	[ -s daemon.pid ] && kill -9 `cat daemon.pid`
+	true
+}
+
 atf_test_case supervisor_pidfile cleanup
 supervisor_pidfile_head() {
 	atf_set "descr" "daemon should write its own pid to a pidfile"
@@ -218,6 +255,7 @@ atf_init_test_cases() {
 	atf_add_test_case newsyslog
 	atf_add_test_case output_file
 	atf_add_test_case restart_child
+	atf_add_test_case restart_hang
 	atf_add_test_case supervisor_pidfile
 	atf_add_test_case supervisor_pidfile_lock
 	atf_add_test_case title