base: Add 'guest' user with no groups, not in sudoers

base/etc/master.passwd

@@ -1,2 +1,3 @@
 root:toor:0:0:Administrator:/home/root:/bin/sh:fancy
 local:local:1000:1000:Local User:/home/local:/bin/sh:fancy
+guest:guest:1001:1001:Guest User:/home/guest:/bin/sh:fancy

base/etc/passwd

@@ -1,3 +1,4 @@
 root:x:0:0:Administrator:/home/root:/bin/sh:fancy
 adm:x:1:1:Administrators:/tmp:/bin/false:nope
 local:x:1000:1000:Local User:/home/local:/bin/sh:fancy
+guest:x:1001:1001:Guest User:/home/guest:/bin/sh:fancy

util/createramdisk.py

@@ -10,6 +10,7 @@ import tarfile
 users = {
     'root': 0,
     'local': 1000,
+    'guest': 1001,
 }
 
 restricted_files = {