adding warning message for operation time

Author: Shefali

src/ServiceManagement/HDInsight/Commands.HDInsight/Cmdlet/SetAzureHDInsightClusterSizeCmdlet.cs

@@ -139,6 +139,7 @@ protected override void EndProcessing()
                     getCommand.CurrentSubscription = currentSubscription;
                     getCommand.Name = Name;
                     var getTask = getCommand.EndProcessing();
+                    this.WriteObject("This operation may take several minutes...");
                     while (!getTask.IsCompleted)
                     {
                         WriteDebugLog();