Add pkg/fall for Fallthrough (#1355)

* Add pkg/fall for Fallthrough

Move this into it's own package to facilitate tests. Important bug
was fixed: make the names fully qualified.

Add fall package to hosts, reverse, etcd, and fix kubernetes and any
tests. The k8s tests are still as-is, might need a future cleanup.

plugin/reverse/reverse_test.go

@@ -24,7 +24,6 @@ func TestReverse(t *testing.T) {
 			Template:     "ip-{ip}.example.org.",
 			RegexMatchIP: regexIP4,
 		}},
-		Fallthrough: false,
 	}
 
 	tests := []struct {