Fix plain XPK command execution

[scaliby]

Fixes / Features

Fixes command execution when running $ xpk.
Previously this was throwing:

AttributeError: 'Namespace' object has no attribute 'dry_run'

Now it works.

[jamOne-]

1. Why doesn't it fail on skip_validation?
2. Curious: what's the output of $ xpk?

[scaliby]

1. Why doesn't it fail on skip_validation?
2. Curious: what's the output of $ xpk?

1. main_args is an empty object when there is no subcommand. I changed to is_dry_run() per what @FIoannides said and it actually started to fail on skip_validation. I reorganized this code a bit so it handles all cases.
2. it throws AttributeError, as in description.

[jamOne-]

I mean, what's the output of xpk after the changes?

[scaliby]

I mean, what's the output of xpk after the changes?

It's the help page