Resources are not cleaned up when repository subpath is empty

[sebastianrosch]

As hinted at in #92, Faros does not delete resources in Kubernetes that were deleted from the repository when there are no other resources in the repository subpath. It just prints no files for subpath '<subpath>'.

In my tests, an empty .yaml file in the subpath was enough for Faros to delete the remaining resources.

[sebastianrosch]

As proposed in #100 and #101, a more explicit delete would be one way to avoid this.

[tshak]

From a safety perspective I actually like this behavior. Maybe the fix is to just improve the error message and (not mutually exclusive) implement the attribute based deletion.