[Bug] Garden exists with 0 exit code on unsupported options and sub-commands

[vvagaytsev]

Bug

Current Behavior

Case 1.
When garden is executed with an unrecognized option and without any command (e.g. garden --bad) it prints the usage help and exists with code 0.

Case 2.
When garden is executed with an unrecognized sub-command (e.g. garden run bad) it prints the usage help and exists with code 0.

Expected behavior

In both cases above garden should exit with code 1 if an unrecognized option or sub-command is passed.

Reproducible example

Run these commands:

# Unrecognized option:
> garden --bad
# usage output omitted
# ...
> echo $?
0   # <- this is wrong

# Unrecognized sub-command:
> garden delete bad
# usage output omitted
# ...
> echo $?
0   # <- this is wrong

Workaround

No

Suggested solution(s)

Implement checks for garden's options inspection and exit with code 1 on unrecognized options.

Note! The old behaviour for other testing scenarios is correct and must be kept:

# Unrecognized (invalid) command:
> garden bad
# usage output omitted
# ...
> echo $?
1

# Unrecognized (invalid) _command_ option:
> garden deploy --bad
# usage output omitted
# ...
> echo $?
1

# Recognized (valid) option:
> garden --help
# usage output omitted
# ...
> echo $?
0

Make sure we have the tests for the scenarios above. Please implement the missing test scenarios if any.

Additional context

This comes from the discussion started in #4868.

Your environment

• OS: all
• How I'm running Kubernetes: does not matter

garden version 0.13.9
garden version 0.12.63