BK8s datasource middleware -- PoC for A records (#153)

* Laying down kubernetes middleware foundation

* Duplicated a bunch of code form etcd middleware
* Duplicated code hacked to compile and load as a separate middleware

* Adding verbose build option to Makefile

* Removing stubzone and tls support

tls and stubzone support was carried over from base etcd middleware code.
Removing to simplify the kube middleware implementation. (For now.)

* Adding conf directory for sample conf files

* Removing stubzone support from query handler

* Remove upstream and proxy from k8s corefile.

Not sure that upstream or proxy makes sense for a k8s backed zone.

* Comment out use of singleflight serialization

* Removing parsing support for "upstream" directive from k8s

* Removing upstream directive parsing code

* Removing CNAME and TXT lookup implementation

* Create README.md

Brain-dump of DNS record name assembly and open work items.

* Adding notes about wildcard handling

* Adding basic k8s API client

* Fleshing out methods on k8s connector

* Remove PathPrefix from middleware init

* Removing incorrect plural

* Adding brute-force k8s service lookup functions

* Initializing k8s API connector during startup

* Hacking around to call k8s connector

* Parsing incoming domain name into serviceName and namespace

* Improving and simplifying k8s zone matching and label segmentation

* Removing unused functions carried over from etcd middleware

* Adding basic return of k8s data to DNS client

* updated debugging println statements to flag with "[debug]"
* removed code in kubernetes.go::Records that was a hold-over from etcd middleware.
* Removed some random exploratory hacking.

* Minior README.md updates

* Updating with demo instructions

* Updating README.md with CoreFile and removing completed TODO items

* Updating conf file and README to reflect DNS response cache works

* Disabling DNS response caching

* Adding debug statement on entry to Records()

* Changing port number in exampes to port 53.

* Misc style and clarity changes

* Removing empty function definitions

* Adding comment to track future cleanup

* Refactoring README to follow style of other middleware

* Exposing dataobject field (typo)

core/setup/kubernetes.go

@@ -0,0 +1,93 @@
+package setup
+
+import (
+//	"crypto/tls"
+//	"crypto/x509"
+    "fmt"
+//	"io/ioutil"
+//	"net"
+//	"net/http"
+//	"time"
+
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/coredns/middleware/kubernetes"
+	k8sc "github.com/miekg/coredns/middleware/kubernetes/k8sclient"
+	"github.com/miekg/coredns/middleware/proxy"
+//	"github.com/miekg/coredns/middleware/singleflight"
+
+	"golang.org/x/net/context"
+)
+
+const defaultK8sEndpoint = "http://localhost:8080"
+
+// Kubernetes sets up the kubernetes middleware.
+func Kubernetes(c *Controller) (middleware.Middleware, error) {
+    fmt.Println("controller %v", c)
+    // TODO: Determine if subzone support required
+
+	kubernetes, err := kubernetesParse(c)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return func(next middleware.Handler) middleware.Handler {
+		kubernetes.Next = next
+		return kubernetes
+	}, nil
+}
+
+func kubernetesParse(c *Controller) (kubernetes.Kubernetes, error) {
+
+    /*
+     * TODO: Remove unused state and simplify.
+     * Inflight and Ctx might not be needed. Leaving in place until
+     * we take a pass at API caching and optimizing connector to the
+     * k8s API. Single flight (or limited upper-bound) for inflight 
+     * API calls may be desirable.
+     */ 
+
+	k8s := kubernetes.Kubernetes{
+        Proxy:      proxy.New([]string{}),
+		Ctx:        context.Background(),
+//		Inflight:   &singleflight.Group{},
+        APIConn:    nil,
+	}
+	var (
+		endpoints     = []string{defaultK8sEndpoint}
+	)
+	for c.Next() {
+		if c.Val() == "kubernetes" {
+			k8s.Zones = c.RemainingArgs()
+			if len(k8s.Zones) == 0 {
+				k8s.Zones = c.ServerBlockHosts
+			}
+			middleware.Zones(k8s.Zones).FullyQualify()
+			if c.NextBlock() {
+				// TODO(miek): 2 switches?
+				switch c.Val() {
+				case "endpoint":
+					args := c.RemainingArgs()
+					if len(args) == 0 {
+						return kubernetes.Kubernetes{}, c.ArgErr()
+					}
+					endpoints = args
+                    k8s.APIConn = k8sc.NewK8sConnector(endpoints[0])
+				}
+				for c.Next() {
+					switch c.Val() {
+					case "endpoint":
+						args := c.RemainingArgs()
+						if len(args) == 0 {
+							return kubernetes.Kubernetes{}, c.ArgErr()
+						}
+						endpoints = args
+					}
+				}
+			}
+			return k8s, nil
+		}
+        fmt.Println("endpoints='%v'", endpoints)
+	}
+	return kubernetes.Kubernetes{}, nil
+}