Handle backspace for k210/qemu platform && Add lots of user tests.

user/src/bin/sleep.rs

@@ -0,0 +1,30 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use user_lib::{sleep, exit, get_time, fork, waitpid};
+
+fn sleepy() {
+    let time: usize = 100;
+    for i in 0..5 {
+        sleep(time);
+        println!("sleep {} x {} msecs.", i + 1, time);
+    }
+    exit(0);
+}
+
+#[no_mangle]
+pub fn main() -> i32 {
+    let current_time = get_time();
+    let pid = fork();
+    let mut xstate: i32 = 0;
+    if pid == 0 {
+        sleepy();
+    }
+    assert!(waitpid(pid as usize, &mut xstate) == pid && xstate == 0);
+    println!("use {} msecs.", get_time() - current_time);
+    println!("sleep pass.");
+    0
+}