Add Azure DNS (#547)

* Add Azure DNS

* Remove unused code

* Fix failing tests and update build

vendor/github.com/Azure/go-autorest/tracing/tracing.go

@@ -0,0 +1,67 @@
+package tracing
+
+// Copyright 2018 Microsoft Corporation
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+
+import (
+	"context"
+	"net/http"
+)
+
+// Tracer represents an HTTP tracing facility.
+type Tracer interface {
+	NewTransport(base *http.Transport) http.RoundTripper
+	StartSpan(ctx context.Context, name string) context.Context
+	EndSpan(ctx context.Context, httpStatusCode int, err error)
+}
+
+var (
+	tracer Tracer
+)
+
+// Register will register the provided Tracer.  Pass nil to unregister a Tracer.
+func Register(t Tracer) {
+	tracer = t
+}
+
+// IsEnabled returns true if a Tracer has been registered.
+func IsEnabled() bool {
+	return tracer != nil
+}
+
+// NewTransport creates a new instrumenting http.RoundTripper for the
+// registered Tracer.  If no Tracer has been registered it returns nil.
+func NewTransport(base *http.Transport) http.RoundTripper {
+	if tracer != nil {
+		return tracer.NewTransport(base)
+	}
+	return nil
+}
+
+// StartSpan starts a trace span with the specified name, associating it with the
+// provided context.  Has no effect if a Tracer has not been registered.
+func StartSpan(ctx context.Context, name string) context.Context {
+	if tracer != nil {
+		return tracer.StartSpan(ctx, name)
+	}
+	return ctx
+}
+
+// EndSpan ends a previously started span stored in the context.
+// Has no effect if a Tracer has not been registered.
+func EndSpan(ctx context.Context, httpStatusCode int, err error) {
+	if tracer != nil {
+		tracer.EndSpan(ctx, httpStatusCode, err)
+	}
+}