func-tests: change answer_count to more general count

tests-extra/tests/dnssec/dnskey_timestamps/test.py

tests-extra/tests/dnssec/none_to_nsec/test.py

tests-extra/tests/dnssec/none_to_nsec3/test.py

tests-extra/tests/dnssec/nsec3_to_nsec/test.py

tests-extra/tests/dnssec/nsec3_to_nsec_ddns/test.py

tests-extra/tests/dnssec/nsec_to_nsec3/test.py

tests-extra/tests/dnssec/nsec_to_nsec3_ddns/test.py

tests-extra/tools/dnstest/response.py