Fix check_beta error if cmd is not in beta args dict.

scripts/cdist

@@ -49,6 +49,7 @@ def check_beta(args_dict):
     # raise error.
     if not args_dict['beta']:
         cmd = args_dict['command']
+        if cmd in BETA_ARGS:
             for arg in BETA_ARGS[cmd]:
                 if arg in args_dict:
                     raise cdist.CdistBetaRequired(cmd, arg)