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/health/setup.go

@@ -0,0 +1,73 @@
+package health
+
+import (
+	"net"
+	"time"
+
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("health", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	addr, err := healthParse(c)
+	if err != nil {
+		return plugin.Error("health", err)
+	}
+
+	h := &health{Addr: addr}
+
+	c.OnStartup(func() error {
+		for he := range healthers {
+			m := dnsserver.GetConfig(c).Handler(he)
+			if x, ok := m.(Healther); ok {
+				h.h = append(h.h, x)
+			}
+		}
+		return nil
+	})
+
+	c.OnStartup(func() error {
+		h.poll()
+		go func() {
+			for {
+				<-time.After(1 * time.Second)
+				h.poll()
+			}
+		}()
+		return nil
+	})
+
+	c.OnStartup(h.Startup)
+	c.OnFinalShutdown(h.Shutdown)
+
+	// Don't do AddMiddleware, as health is not *really* a plugin just a separate webserver running.
+	return nil
+}
+
+func healthParse(c *caddy.Controller) (string, error) {
+	addr := ""
+	for c.Next() {
+		args := c.RemainingArgs()
+
+		switch len(args) {
+		case 0:
+		case 1:
+			addr = args[0]
+			if _, _, e := net.SplitHostPort(addr); e != nil {
+				return "", e
+			}
+		default:
+			return "", c.ArgErr()
+		}
+	}
+	return addr, nil
+}