Update kasp test with CDNSKEY checks
Add checks to the kasp system test to verify CDNSKEY publication. This test is not entirely complete, because when there is a CDNSKEY available but there should not be one for KEY N, it is hard to tell whether the existing CDNSKEY actually belongs to KEY N or another key.
The check works if we expect a CDNSKEY although we cannot guarantee that the CDNSKEY is correct: The test verifies existence, not correctness of the record.
Closes #1545 (closed)