func-test: split dnstest to submodules

tests-extra/functional/functests.py

tests-extra/functional/tests/axfr/bind_knot/test.py

tests-extra/functional/tests/axfr/interrupt/test.py

tests-extra/functional/tests/axfr/knot_bind/test.py

tests-extra/functional/tests/axfr/knot_knot/test.py

tests-extra/functional/tests/basic/flags/test.py

tests-extra/functional/tests/basic/rcode/test.py

tests-extra/functional/tests/chaos/ident/test.py

tests-extra/functional/tests/chaos/version/test.py

tests-extra/functional/tests/ddns/forward/test.py

tests-extra/functional/tests/ddns/prereq/test.py

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

tests-extra/functional/tests/edns/nsid/test.py

tests-extra/functional/tests/edns/payload/test.py

tests-extra/functional/tests/records/obsolete/test.py

...extra/functional/tests/records/out-of-zone-master/test.py

...-extra/functional/tests/records/out-of-zone-slave/test.py

tests-extra/functional/tests/security/dnsheader/test.py

tests-extra/functional/tests/security/protos/test.py

tests-extra/functional/tools/dnstest/__init__.py