Use server block defaults (#894)

* mw/k8s: Test Federation parsing

The test case was there, but there was nothing testing it?!?!?!
Add it and split it out of the main setup test which is too long
already.

Also allow kubernetes a not have a ZONE, just default to the serverblock
in that case. Remove test that was blocking that.

Cleanup up the readme more.

* rewrite README

middleware/kubernetes/README.md

@@ -10,8 +10,17 @@ to deploy CoreDNS in Kubernetes](https://github.com/coredns/deployment/tree/mast
 
 ## Syntax
 
+~~~
+kubernetes [ZONES...]
+~~~
+
+With only the directive specified, the *kubernetes* middleware will default to the zone specified in
+the server's block. It will handle all queries in that zone and connect to Kubernetes in-cluster. It
+will not provide PTR records for services, or A records for pods. If **ZONES** is used is specifies
+all the zones the middleware should be authoritative for.
+
 ```
-kubernetes ZONE [ZONE...] [
+kubernetes [ZONES...] {
 	resyncperiod DURATION
 	endpoint URL
 	tls CERT KEY CACERT]
@@ -23,7 +32,6 @@ kubernetes ZONE [ZONE...] [
 	fallthrough
 }
 ```
-
 * `resyncperiod` specifies the Kubernetes data API **DURATION** period.
 * `endpoint` specifies the **URL** for a remove k8s API endpoint.
    If omitted, it will connect to k8s in-cluster using the cluster service account.
@@ -63,13 +71,10 @@ kubernetes ZONE [ZONE...] [
 
 ## Examples
 
-**Example 1:** This is a minimal configuration with no options other than zone. It will handle all queries in the `cluster.local` zone and connect to Kubernetes in-cluster, but it will not provide PTR records for services, or A records for pods.
-
-	kubernetes cluster.local
-
-**Example 2:** Handle all queries in the `cluster.local` zone. Connect to Kubernetes in-cluster.
- Handle all `PTR` requests for `10.0.0.0/16` . Verify the existence of pods when answering pod
- requests.  Resolve upstream records against `10.102.3.10`.
+Handle all queries in the `cluster.local` zone. Connect to Kubernetes in-cluster.
+Als handl all `PTR` requests for `10.0.0.0/16` . Verify the existence of pods when answering pod
+requests. Resolve upstream records against `10.102.3.10`. Note we show the entire server block
+here:
 
     10.0.0.0/16 cluster.local {
         kubernetes {
@@ -78,38 +83,36 @@ kubernetes ZONE [ZONE...] [
         }
     }
 
-**Selective Exposure Example:** Handle all queries in the `cluster.local` zone. Connect to Kubernetes in-cluster. Only expose objects in the test and staging namespaces.
-  Resolve upstream records using the servers configured in `/etc/resolv.conf`.
+Or you can selective expose some namespaces:
 
 	kubernetes cluster.local {
 		namespaces test staging
+    }
 
-**Federation Example:** Handle all queries in the `cluster.local` zone. Connect to Kubernetes in-cluster. Handle federated service requests in the `prod` and `stage` federations.
-  Resolve upstream records using the servers configured in `/etc/resolv.conf`.
+If you want to use federation, just use the `federation` option. Here we handle all service requests
+in the `prod` and `stage` federations. We resolve upstream records using the servers configured in
+`/etc/resolv.conf`.
 
-    cluster.local {
-        kubernetes {
+    . {
+        kubernetes cluster.local {
 		    federation prod prod.feddomain.com
 		    federation stage stage.feddomain.com
 		    upstream /etc/resolv.conf
     	}
     }
 
-**Out-Of-Cluster Example:** Handle all queries in the `cluster.local` zone. Connect to Kubernetes from outside the cluster.
-  Verify the existence of pods when answering pod requests.  Resolve upstream records against `10.102.3.10`.
+And finally we connect to Kubernetes from outside the cluster:
 
 	kubernetes cluster.local {
 		endpoint https://k8s-endpoint:8443
 		tls cert key cacert
-		pods verified
-		upstream 10.102.3.10:53
 	}
 
 
-
 ## Wildcard
 
-Some query labels accept a wildcard value to match any value.  If a label is a valid wildcard (\*, or the word "any"), then that label will match all values.  The labels that accept wildcards are:
+Some query labels accept a wildcard value to match any value.  If a label is a valid wildcard (\*,
+or the word "any"), then that label will match all values.  The labels that accept wildcards are:
 
  * _service_ in an `A` record request: _service_.namespace.svc.zone.
    * e.g. `*.ns.svc.myzone.local`

middleware/kubernetes/setup.go

@@ -87,10 +87,6 @@ func kubernetesParse(c *caddy.Controller) (*Kubernetes, error) {
 				}
 			}
 
-			if k8s.Zones == nil || len(k8s.Zones) < 1 {
-				return nil, errors.New("zone name must be provided for kubernetes middleware")
-			}
-
 			k8s.primaryZone = -1
 			for i, z := range k8s.Zones {
 				if strings.HasSuffix(z, "in-addr.arpa.") || strings.HasSuffix(z, "ip6.arpa.") {