hostname: bug fix for non-windows xgethostname and add test case

Cstr::from_bytes_with_nul needs input bytes null terminated. Current
version does not include the last null byte, hence
Cstr::from_bytes_with_nul will panic with error 'FromBytesWithNulError {
kind: NotNulTerminated }'

tests/test_hostname.rs

@@ -0,0 +1,12 @@
+use common::util::*;
+
+#[test]
+fn test_hostname() {
+    let ls_default_res = new_ucmd!().succeeds();
+    let ls_short_res = new_ucmd!().arg("-s").succeeds();
+    let ls_domain_res = new_ucmd!().arg("-d").succeeds();
+
+    assert!(ls_default_res.stdout.len() >= ls_short_res.stdout.len());
+    assert!(ls_default_res.stdout.len() >= ls_domain_res.stdout.len());
+}
+

tests/tests.rs

@@ -91,6 +91,7 @@ generic! {
     "tsort", test_tsort;
     "unexpand", test_unexpand;
     "uniq", test_uniq;
+    "wc", test_wc;
     // Be aware of the trailing semicolon after the last item
-    "wc", test_wc
+    "hostname", test_hostname
 }