Stacktrace when executing oríon without arguments

[Thomsch]

When executing orion without arguments, I get a stacktrace:

~$ orion
Traceback (most recent call last):
  File "/home/thomsch/venv/pycharm/bin/orion", line 10, in <module>
    sys.exit(main())
  File "/home/thomsch/venv/pycharm/lib/python3.7/site-packages/orion/core/cli/__init__.py", line 39, in main
    orion_parser.execute(argv)
  File "/home/thomsch/venv/pycharm/lib/python3.7/site-packages/orion/core/cli/base.py", line 73, in execute
    args, function = self.parse(argv)
  File "/home/thomsch/venv/pycharm/lib/python3.7/site-packages/orion/core/cli/base.py", line 67, in parse
    function = args.pop('func')
KeyError: 'func'

The expected behavior is to execute a default behaviour (for example ls lists the files and folder in the current directory) or show a helpful message to the user, usually the content of --help.

In orion's context, I believe showing the help would be the most appropriate action to execute.

[Thomsch]

Handle orion without arguments

[Thomsch]

This indesirable behaviour is also present for the following subcommands:

• init_only
• hunt
• db
• insert
• info

[Thomsch]

https://github.com/Epistimio/orion/issues/328

[Thomsch]

https://github.com/Epistimio/orion/issues/328

[Thomsch]

https://github.com/Epistimio/orion/issues/328

[Thomsch]

Fixed in #408