test/vfork00: directly _exit() instead of exec() in vforked proccess

execlp() fails when we run vfork00 test inside namespace because we don't have
'/bin/true' there. Instead of execlp() in vfork-child we can just _exit().
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm/static/vfork00.c

@@ -37,9 +37,9 @@ int main(int argc, char ** argv)
 		/* wait for signal in _both_ branches */
 		test_waitsig();
 
-		/* vforked guy shouldn't return, hence we exec() */
+		/* vforked guy shouldn't return, hence we _exit() */
 		if (pid == 0)
-			execlp("/bin/true", "true", NULL);
+			_exit(0);
 
 		if (wait(&ret2) != pid)
 			ret = errno;