coredns: default Corefile (#265)

When no Corefile is given, default to loading the whoami middleware on
the default port (2053).  Also add back the -port flag that allows you
to override the default port.

Further cleanup the startup messages and use caddy's OnStartupComplete()
to blurp out which zones and ports we have.  These can be suppressed
with the -quiet flag.

Normal startup:

miek.nl.:1053
miek.nl2.:1053
example.org.:1054
2016/09/17 20:41:19 [INFO] CoreDNS-001 starting
CoreDNS-001 starting

with the -quiet flag:

2016/09/17 20:41:34 [INFO] CoreDNS-001 starting

core/dnsserver/register.go

@@ -1,6 +1,7 @@
 package dnsserver
 
 import (
+	"flag"
 	"fmt"
 	"net"
 	"time"
@@ -12,19 +13,15 @@ import (
 const serverType = "dns"
 
 func init() {
+	flag.StringVar(&Port, "port", DefaultPort, "Default port")
+	flag.BoolVar(&Quiet, "quiet", false, "Quiet mode (no initialization output)")
+
 	caddy.RegisterServerType(serverType, caddy.ServerType{
 		Directives: func() []string { return directives },
 		DefaultInput: func() caddy.Input {
-			if Port == DefaultPort && Zone != "" {
-				return caddy.CaddyfileInput{
-					Filepath:       "Corefile",
-					Contents:       nil,
-					ServerTypeName: serverType,
-				}
-			}
 			return caddy.CaddyfileInput{
 				Filepath:       "Corefile",
-				Contents:       nil,
+				Contents:       []byte(".:" + Port + " {\nwhoami\n}\n"),
 				ServerTypeName: serverType,
 			}
 		},
@@ -63,7 +60,6 @@ func (h *dnsContext) InspectServerBlocks(sourceFile string, serverBlocks []caddy
 			s.Keys[i] = za.String()
 			if v, ok := dups[za.Zone]; ok {
 				return nil, fmt.Errorf("cannot serve %s - zone already defined for %v", za, v)
-
 			}
 			dups[za.Zone] = za.String()
 
@@ -71,7 +67,6 @@ func (h *dnsContext) InspectServerBlocks(sourceFile string, serverBlocks []caddy
 			cfg := &Config{
 				Zone: za.Zone,
 				Port: za.Port,
-				// TODO(miek): more?
 			}
 			h.saveConfig(za.String(), cfg)
 		}
@@ -129,8 +124,6 @@ func groupConfigsByListenAddr(configs []*Config) (map[string][]*Config, error) {
 }
 
 const (
-	// DefaultZone is the default zone.
-	DefaultZone = "."
 	// DefaultPort is the default port.
 	DefaultPort = "2053"
 	// DefaultRoot is the default root folder.
@@ -141,14 +134,15 @@ const (
 // command line flags, etc.
 var (
 	// Root is the site root
+	// TODO(miek): double check if this is used and if we want to use it.
 	Root = DefaultRoot
 
-	// Host is the site host
-	Zone = DefaultZone
-
 	// Port is the site port
 	Port = DefaultPort
 
 	// GracefulTimeout is the maximum duration of a graceful shutdown.
 	GracefulTimeout time.Duration
+
+	// Quiet mode will not show any informative output on initialization.
+	Quiet bool
 )