Create tests which verify that Reclass features continue working as expected

[simu]

Context

We're relying on quite a few features in Reclass (provided via Kapitan) for Commodore to work correctly. However, we currently don't have any tests that fail reliably when there's regressions in Reclass, see e.g. #324, #326 and #327.

We should implement tests which exercise relevant features of Kapitan and Reclass, at least the following:

• Relative class references
• Removing entries from the applications array
• Reclass accepts classes with extension .yml and .yaml.

The preferred way to test these features would be to generate inventory hierarchies using the features we're interested in and verifying that rendering the Kapitan inventory for such produces the correct results.

Alternatives

Keep the status quo: we hope for the best when updating Kapitan and Reclass and deal with regresions as we find them.