Added support for Haystack tracing

pkg/tracing/haystack/logger.go

@@ -0,0 +1,25 @@
+package haystack
+
+import (
+	"github.com/containous/traefik/pkg/log"
+)
+
+/*NullLogger does nothing*/
+type haystackLogger struct {
+	logger log.Logger
+}
+
+/*Error prints the error message*/
+func (l haystackLogger) Error(format string, v ...interface{}) {
+	l.logger.Errorf(format, v)
+}
+
+/*Info prints the info message*/
+func (l haystackLogger) Info(format string, v ...interface{}) {
+	l.logger.Infof(format, v)
+}
+
+/*Debug prints the info message*/
+func (l haystackLogger) Debug(format string, v ...interface{}) {
+	l.logger.Debug(format, v)
+}