Create a small speedup running the tests:
PASS
ok github.com/miekg/coredns/test 10.329s
PASS
ok github.com/miekg/coredns/test 6.079s
Skip the etcd ones. Doing the middleware/*/*_test ones doesn't yield
any speedup as these are still done on a per directory basis.
The DS record is handled specially in the server ServeDNS mux, but there
was no code that actually called the correct middleware handler chain
when encountering a DS.
This PR fixes that behavoir, additonal bugs has been files to look into
how we are handling delegation (secure and non-secure ones).