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

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) {