tests: Fix /general/nm_utils_kill_child race

/general/nm_utils_kill_child: **
GLib:ERROR:test-general-with-expect.c:105:test_nm_utils_kill_child_sync_do: Did not see expected message NetworkManager-DEBUG: *kill child process 'test-s-1-1' (*): waiting up to 500 milliseconds for process to terminate normally after sending SIGTERM (15)...
Aborted

The first test case assumes the child does not go away immediately after being
delivered a TERM signal. Add some delay to its teardown code path, so that NM
will set up the timeout the test expects.

src/tests/test-general-with-expect.c

@@ -188,6 +188,7 @@ test_nm_utils_kill_child (void)
 	char *argv1[] = {
 			"sh",
 			"-c",
+			"trap \"sleep 0.3; exit 10\" EXIT; "
 			"sleep 100000; exit $? #" TEST_TOKEN,
 			NULL,
 		};