Command 'run' says nothing if the plan was mistyped

[atimin]

Describe the bug
Command 'run' should show message if a user types a wrong test plan.

To Reproduce
Steps to reproduce the behavior:

1. I have only one test plan 'feature_1.plan_1'
2. Input command python -m nitpicker run bla.bla.bla
3. Nothing happens

Expected behavior
I'd like to see an error message.

System (please complete the following information):

• Version 0.3.0