Use useradd rather than adduser to create users

Better suited for scripting use. adduser also seemed to
cause issues when root user's password had expired, so let's see
if useradd fixes that!

tljh/user.py

@@ -22,10 +22,7 @@ def ensure_user(username):
         pass
 
     subprocess.check_call([
-        'adduser',
+        'useradd',
-        '--disabled-password',
-        '--force-badname',
-        '--quiet',
         username
     ])
 
@@ -51,16 +48,9 @@ def ensure_group(groupname):
     """
     Ensure given group exists
     """
-    try:
-        grp.getgrnam(groupname)
-        # Group exists, nothing to do!
-        return
-    except KeyError:
-        pass
-
     subprocess.check_call([
-        'addgroup',
+        'groupadd',
-        '--quiet',
+        '--force',
         groupname
     ])