Teach certbot about certbot-auto's new --pypi-mirror option so it doesn't throw an unknown-arg error.

certbot/cli.py

@@ -1024,6 +1024,11 @@ def prepare_and_parse_args(plugins, args, detect_defaults=False):  # pylint: dis
         help="(certbot-auto only) prevent the certbot-auto script from"
              " installing OS-level dependencies (default: Prompt to install "
              " OS-wide dependencies, but exit if the user says 'No')")
+    helpful.add(
+        "automation", "--pypi-mirror", action="store_true",
+        default=flag_default("pypi_mirror"),
+        help="(certbot-auto only) use an alternative Python package server "
+             "that is reachable from China")
     helpful.add(
         ["automation", "renew", "certonly", "run"],
         "-q", "--quiet", dest="quiet", action="store_true",

certbot/constants.py

@@ -44,6 +44,7 @@ CLI_DEFAULTS = dict(
     os_packages_only=False,
     no_self_upgrade=False,
     no_bootstrap=False,
+    pypi_mirror=False,
     quiet=False,
     staging=False,
     debug=False,