Cache the size and the do bit whenever someone asked for it. We can

probably add more:



PASS

BenchmarkStateDo-4  	100000000	        11.9 ns/op

BenchmarkStateSize-4	 5000000	       265 ns/op

ok  	github.com/miekg/coredns/middleware	2.828s



PASS

BenchmarkStateDo-4  	1000000000	         2.86 ns/op

BenchmarkStateSize-4	500000000	         3.10 ns/op

ok  	github.com/miekg/coredns/middleware	5.032s



This PR also includes some testing cleanups as well.