mw/kubernetes: remove federation and cidr (#916)

* mw/kubernetes: remove federation and cidr

Remove both as we have a corefile syntax change that handles cidr and
remove federation because that is going to be its own middleware.

* backwards incompat changes

This PR:
* removes cidr from kubernetes (core Corefile feature now)
* removes federation from kubernets (comes back as new middleware)
* [remove autopath - which was already gone, so that already was
  backwards incompat]
* adds `fallthrough` to the *etcd* middleware and makes you enable it.
* Fail on unknown properties
* documentation
* Disable TestHealthCheck as it uses realtime and fails

test/etcd_test.go

@@ -42,6 +42,7 @@ func TestEtcdStubAndProxyLookup(t *testing.T) {
         path /skydns
         endpoint http://localhost:2379
         upstream 8.8.8.8:53 8.8.4.4:53
+	fallthrough
     }
     proxy . 8.8.8.8:53
 }`