pkg/log: fix data race on d (#2698)

* pkg/log: fix data race on d

Wrap d in a mutex to prevent data race. This makes is slower, but this
is a debugging aid anyway. It's not used normally.

Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix tests compilation

Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix test compile

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/pkg/log/log_test.go

@@ -18,7 +18,7 @@ func TestDebug(t *testing.T) {
 	}
 	f.Reset()
 
-	D = true
+	D.Set()
 	Debug("debug")
 	if x := f.String(); !strings.Contains(x, debug+"debug") {
 		t.Errorf("Expected debug log to be %s, got %s", debug+"debug", x)
@@ -29,7 +29,7 @@ func TestDebugx(t *testing.T) {
 	var f bytes.Buffer
 	golog.SetOutput(&f)
 
-	D = true
+	D.Set()
 
 	Debugf("%s", "debug")
 	if x := f.String(); !strings.Contains(x, debug+"debug") {