Now sleep test sleeps 5secs.

user/src/bin/sleep.rs

@@ -7,7 +7,7 @@ extern crate user_lib;
 use user_lib::{sleep, exit, get_time, fork, waitpid};
 
 fn sleepy() {
-    let time: usize = 100;
+    let time: usize = 1000;
     for i in 0..5 {
         sleep(time);
         println!("sleep {} x {} msecs.", i + 1, time);