Updated forkbomb to better detect success

Previously, we were relying on subpage allocator failing to signal
that forkbomb was succeeding. However, there are cases where the
subpage allocator never fails but the test is still progressing fine.

This commit moves the secure print into forkbomb itself and changes
the test constraints to ensure that forkbomb runs for a certain amount
of time without crashing

userland/testbin/forkbomb/forkbomb.c

@@ -49,6 +49,10 @@
 
 #include <unistd.h>
 #include <err.h>
+#include <time.h>
+#include <test161/test161.h>
+
+#define TEST_DURATION 10
 
 static volatile int pid;
 
@@ -57,9 +61,17 @@ main(void)
 {
 	int i;
 
+	time_t start_time_s, time_now_s;
+	unsigned long start_time_ns, time_now_ns;
+	__time(&start_time_s, &start_time_ns);
 	while (1) {
 		fork();
 
+		__time(&time_now_s, &time_now_ns);
+		if(time_now_s - start_time_s > TEST_DURATION) {
+			success(TEST161_SUCCESS, SECRET, "/testbin/forkbomb");
+		}
+
 		pid = getpid();
 
 		/* Make sure each fork has its own address space. */