challenge: add shadow file

challenge.yml

@@ -42,7 +42,7 @@ files:
     mode: "0644"
   - path: etc/passwd
     contents: |
-      root:x:0:0:root:/root:/bin/bash
+      root:x:0:0:root:/root:/bin/ash
       bin:x:1:1:bin:/bin:/bin/false
       daemon:x:2:2:daemon:/sbin:/bin/false
       adm:x:3:4:adm:/var/adm:/bin/false
@@ -52,8 +52,22 @@ files:
       halt:x:7:0:halt:/sbin:/sbin/halt
       news:x:9:13:news:/var/spool/news:/bin/false
       uucp:x:10:14:uucp:/var/spool/uucp:/bin/false
-      operator:x:11:0:operator:/root:/bin/bash
+      operator:x:11:0:operator:/root:/bin/ash
     mode: "0644"
+  - path: etc/shadow
+    contents: |
+      root:!::0::::::
+      bin:!::0::::::
+      daemon:!::0::::::
+      adm:!::0::::::
+      lp:!::0::::::
+      sync:!::0::::::
+      shutdown:!::0::::::
+      halt:!::0::::::
+      news:!::0::::::
+      uucp:!::0::::::
+      operator:!::0::::::
+    mode: "0640"
   - path: etc/periodic/15min/netreboot
     contents: |
       #!/bin/sh