Update all plugins to use plugin/pkg/log (#1694)

* Update all plugins to use plugin/pkg/log

I wish this could have been done with sed. Alas manually changed all
callers to use the new plugin/pkg/log package.

* Error -> Info

* Add docs to debug plugin as well

plugin/cache/cache.go

@@ -4,11 +4,11 @@ package cache
 import (
 	"encoding/binary"
 	"hash/fnv"
-	"log"
 	"time"
 
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/pkg/cache"
+	"github.com/coredns/coredns/plugin/pkg/log"
 	"github.com/coredns/coredns/plugin/pkg/response"
 	"github.com/coredns/coredns/request"
 
@@ -178,13 +178,13 @@ func (w *ResponseWriter) set(m *dns.Msg, key int, mt response.Type, duration tim
 	case response.OtherError:
 		// don't cache these
 	default:
-		log.Printf("[WARNING] Caching called with unknown classification: %d", mt)
+		log.Warningf("Caching called with unknown classification: %d", mt)
 	}
 }
 
 // Write implements the dns.ResponseWriter interface.
 func (w *ResponseWriter) Write(buf []byte) (int, error) {
-	log.Print("[WARNING] Caching called with Write: not caching reply")
+	log.Warning("Caching called with Write: not caching reply")
 	if w.prefetch {
 		return 0, nil
 	}

plugin/cache/cache_test.go

@@ -1,8 +1,6 @@
 package cache
 
 import (
-	"io/ioutil"
-	"log"
 	"testing"
 	"time"
 
@@ -162,8 +160,6 @@ func TestCache(t *testing.T) {
 
 	c, crr := newTestCache(maxTTL)
 
-	log.SetOutput(ioutil.Discard)
-
 	for _, tc := range cacheTestCases {
 		m := tc.in.Msg()
 		m = cacheMsg(m, tc)