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/root/root.go

@@ -1,11 +1,11 @@
 package root
 
 import (
-	"log"
 	"os"
 
 	"github.com/coredns/coredns/core/dnsserver"
 	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/log"
 
 	"github.com/mholt/caddy"
 )
@@ -33,7 +33,7 @@ func setup(c *caddy.Controller) error {
 		if os.IsNotExist(err) {
 			// Allow this, because the folder might appear later.
 			// But make sure the user knows!
-			log.Printf("[WARNING] Root path does not exist: %s", config.Root)
+			log.Warningf("Root path does not exist: %s", config.Root)
 		} else {
 			return plugin.Error("root", c.Errf("unable to access root path '%s': %v", config.Root, err))
 		}

plugin/root/root_test.go

@@ -3,7 +3,6 @@ package root
 import (
 	"fmt"
 	"io/ioutil"
-	"log"
 	"os"
 	"path/filepath"
 	"strings"
@@ -15,8 +14,6 @@ import (
 )
 
 func TestRoot(t *testing.T) {
-	log.SetOutput(ioutil.Discard)
-
 	// Predefined error substrings
 	parseErrContent := "Error during parsing:"
 	unableToAccessErrContent := "unable to access root path"