tests: add test that journald keeps fds over termination by signal

This test fails before previous commit, and passes with it.

(cherry picked from commit bff653e)
(cherry picked from commit ee8f69a)
Resolves: #1757704

test/TEST-04-JOURNAL/test-journal.sh

@@ -22,5 +22,13 @@ sleep 3
 systemctl stop forever-print-hola
 [[ ! -f "/i-lose-my-logs" ]]
 
+# https://github.com/systemd/systemd/issues/4408
+rm -f /i-lose-my-logs
+systemctl start forever-print-hola
+sleep 3
+systemctl kill --signal=SIGKILL systemd-journald
+sleep 3
+[[ ! -f "/i-lose-my-logs" ]]
+
 touch /testok
 exit 0