Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/kubernetes/local.go

@@ -0,0 +1,40 @@
+package kubernetes
+
+import "net"
+
+func localPodIP() net.IP {
+	addrs, err := net.InterfaceAddrs()
+	if err != nil {
+		return nil
+	}
+
+	for _, addr := range addrs {
+		ip, _, _ := net.ParseCIDR(addr.String())
+		ip = ip.To4()
+		if ip == nil || ip.IsLoopback() {
+			continue
+		}
+		return ip
+	}
+	return nil
+}
+
+func (k *Kubernetes) localNodeName() string {
+	localIP := k.interfaceAddrsFunc()
+	if localIP == nil {
+		return ""
+	}
+
+	// Find endpoint matching localIP
+	endpointsList := k.APIConn.EndpointsList()
+	for _, ep := range endpointsList.Items {
+		for _, eps := range ep.Subsets {
+			for _, addr := range eps.Addresses {
+				if localIP.Equal(net.ParseIP(addr.IP)) {
+					return *addr.NodeName
+				}
+			}
+		}
+	}
+	return ""
+}