Move print to bin/vcloud-walker

This makes walk method testable. Also adds a test for it. It's not a great test because the data is mocked, but it acts as a check that the correct methods are being called.

The error message when not one of the valid calls has been removed. Will be returned in a later commit.
Add back error message

It is just being printed out here. Could be handled more elegantly.
Change all method to organization

To enable removal of case statement in walker.rb. This is the only method name that differs from the input.

I have changed this in Thor as well, though the plan is for Methadone to replace Thor.
Replace case statement

Thanks @snehaso!