Add test cases that use DNSSEC signing

Add test cases that use DNSSEC signing

Add two new masterformat tests that use signing. In the case of
'under-limit-kasp', the signing will keep the number of records in the
RRset under the limit. In the case of 'on-limit-kasp', the signing
will push the number of records in the RRset over the limit, because
of the added RRSIG record.

(cherry picked from commit 4c677882e66883670990a771337ecbb5206a6faa)