Unit tests for Azure scenarios (#495)

* Test firewall rule handling is able to process through the service layer

* Additional tests for authentication and the resource wrapper code

* Positive test case for CreateFirewallRule

* Fixed copyright and usings

src/Microsoft.SqlTools.ResourceProvider.DefaultImpl/AzureResourceWrapper.cs

@@ -81,7 +81,7 @@ namespace Microsoft.SqlTools.ResourceProvider.DefaultImpl
                 {
                     this.resourceGroupName = ParseResourceGroupNameFromId();
                 }
-                return this.resourceGroupName;
+                return this.resourceGroupName ?? string.Empty;
             }
             set
             {