TT#142600 Exit explicitly from the cleanup signal handler

The handler needs to exit explicitly, otherwise we will continue
execution as usual. (These signals are trappable and as such will
not terminate no matter what.)

Fixes: commit a137c6a853
Change-Id: If0e5ad75170ef53eb4cda18d5b20387699909577
(cherry picked from commit a335d5d972)

dhtest.c

@@ -113,6 +113,7 @@ static void cleanup(void) {
 static void sigcleanup(int sig) {
 	fprintf(stderr, "signal %s received, exiting\n", strsignal(sig));
 	cleanup();
+	exit(0);
 }
 
 static void sigabort(int sig) {