update the fix of the multiple x-ms-unique-id values issue

Author: YanaXu

src/Accounts/Accounts/CommonModule/AzModule.cs

@@ -100,7 +100,6 @@ public void OnModuleLoad(string resourceId, string moduleName, PipelineChangeDel
         {
             // this will be called once when the module starts up 
             // the common module can prepend or append steps to the pipeline at this point.
-            prependStep(UniqueId.Instance.SendAsync);
         }
 
         /// <summary>

src/Accounts/Accounts/CommonModule/ContextAdapter.cs

@@ -73,6 +73,7 @@ internal string SelectedProfile
         /// <param name="appendStep">a delegate which allows the module to append a step in the HTTP Pipeline</param>
         public void OnNewRequest(InvocationInfo invocationInfo, string correlationId, string processRecordId, PipelineChangeDelegate prependStep, PipelineChangeDelegate appendStep)
         {
+            prependStep(UniqueId.Instance.SendAsync);
             appendStep(new UserAgent(invocationInfo).SendAsync);
             appendStep(this.SendHandler(GetDefaultContext(_provider, invocationInfo), AzureEnvironment.Endpoint.ActiveDirectoryServiceEndpointResourceId));
         }

src/Accounts/Accounts/CommonModule/UniqueId.cs

@@ -43,11 +43,8 @@ public class UniqueId
         /// <returns>Amended pipeline for retrieving a response</returns>
         public Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken token, Action cancel, SignalDelegate signal, NextDelegate next)
         {
-            if (!request.Headers.Contains("x-ms-unique-id"))
-            {
-                // add a header...
-                request.Headers.Add("x-ms-unique-id", Interlocked.Increment(ref this.count).ToString());
-            }
+            // add a header...
+            request.Headers.Add("x-ms-unique-id", Interlocked.Increment(ref this.count).ToString());
             // continue with pipeline.
             return next(request, token, cancel, signal);
         }