Use logging (#1718)

* update docs

* plugins: use plugin specific logging

Hooking up pkg/log also changed NewWithPlugin to just take a string
instead of a plugin.Handler as that is more flexible and for instance
the Root "plugin" doesn't implement it fully.

Same logging from the reload plugin:

.:1043
2018/04/22 08:56:37 [INFO] CoreDNS-1.1.1
2018/04/22 08:56:37 [INFO] linux/amd64, go1.10.1,
CoreDNS-1.1.1
linux/amd64, go1.10.1,
2018/04/22 08:56:37 [INFO] plugin/reload: Running configuration MD5 = ec4c9c55cd19759ea1c46b8c45742b06
2018/04/22 08:56:54 [INFO] Reloading
2018/04/22 08:56:54 [INFO] plugin/reload: Running configuration MD5 = 9e2bfdd85bdc9cceb740ba9c80f34c1a
2018/04/22 08:56:54 [INFO] Reloading complete

* update docs

* better doc

2 files changed, 3 insertions, 16 deletions

diff --git a/plugin/pkg/log/plugin.go b/plugin/pkg/log/plugin.go
index c79d657c7..354c19d3f 100644
--- a/plugin/pkg/log/plugin.go
+++ b/plugin/pkg/log/plugin.go
@@ -3,8 +3,6 @@ package log
 import (
 	"fmt"
 	golog "log"
-
-	"github.com/coredns/coredns/plugin"
 )
 
 // P is a logger that includes the plugin doing the logging.
@@ -12,9 +10,9 @@ type P struct {
 	plugin string
 }
 
-// NewWithPlugin return a logger that shows the plugin that logs the message.
+// NewWithPlugin returns a logger that includes "plugin/name: " in the log message.
 // I.e [INFO] plugin/<name>: message.
-func NewWithPlugin(h plugin.Handler) P { return P{h.Name()} }
+func NewWithPlugin(name string) P { return P{name} }
 
 func (p P) logf(level, format string, v ...interface{}) {
 	s := level + pFormat(p.plugin) + fmt.Sprintf(format, v...)
diff --git a/plugin/pkg/log/plugin_test.go b/plugin/pkg/log/plugin_test.go
index a7799322e..b24caa48b 100644
--- a/plugin/pkg/log/plugin_test.go
+++ b/plugin/pkg/log/plugin_test.go
@@ -2,28 +2,17 @@ package log
 
 import (
 	"bytes"
-	"context"
 	golog "log"
 	"strings"
 	"testing"
-
-	"github.com/miekg/dns"
 )
 
-type p struct{}
-
-func (p p) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
-	return 0, nil
-}
-
-func (p p) Name() string { return "testplugin" }
-
 func TestPlugins(t *testing.T) {
 	var f bytes.Buffer
 	const ts = "test"
 	golog.SetOutput(&f)
 
-	lg := NewWithPlugin(p{})
+	lg := NewWithPlugin("testplugin")
 
 	lg.Info(ts)
 	if x := f.String(); !strings.Contains(x, "plugin/testplugin") {