Comment 2 for bug 1778536

The cause is the prefix matching of ArgumentParser.

https://docs.python.org/3.6/library/argparse.html#argument-abbreviations-prefix-matching

IMO, there are 2 ways to fix it.

1. Set 'allow_abbrev' to False

  But it is supported since python 3.5.
  It will not be fixed in python2.7.

  https://docs.python.org/3.6/library/argparse.html#allow-abbrev

2. rename '--endpoint-override' to '--os-endpoint-override'