Convert some special kasp test cases to pytest

Convert some special kasp test cases to pytest

This converts a special characters test case, a max-zone-ttl error
check, and two cases of insecure zones.

We no longer assert for having more than one DNSKEY and/or RRSIG
records. If the zone is insecure, this is no longer always true. And
we already check for the expected number of records in the
check_dnskeys/check_signatures functions.

(cherry picked from commit 07ac0e603633a701b35c92de2e3b27dc2643dcba)