r/template_deployment: fixing support for nested template deployments

[tombuildsstuff]

As a part of switching over to the new Authentication library, we switched to using the Profile for resources. In retrospect it appears this broke support for Nested Template Deployments, which require an API version of 2017-05-10 or later, but the profile being used uses the API version 2016-02-01.

As such this PR vendors version 2018-05-01 of the Resources SDK such that this is now fixed. We were missing a test for Nested Template Deployments - but I've added one which confirms the bug & fix:

This new test currently fails on master:

$ acctests azurerm TestAccAzureRMTemplateDeployment_nestedTemplate
=== RUN   TestAccAzureRMTemplateDeployment_nestedTemplate
=== PAUSE TestAccAzureRMTemplateDeployment_nestedTemplate
=== CONT  TestAccAzureRMTemplateDeployment_nestedTemplate
--- FAIL: TestAccAzureRMTemplateDeployment_nestedTemplate (71.60s)
    testing.go:538: Step 0 error: Error applying: 1 error(s) occurred:

        * azurerm_template_deployment.test: 1 error(s) occurred:

        * azurerm_template_deployment.test: Error creating deployment: resources.DeploymentsClient#CreateOrUpdate: Failure sending request: StatusCode=0 -- Original Error: Code="InvalidTemplate" Message="Deployment template validation failed: 'The template resource 'nested-template-deployment' at line '1' and column '176' is invalid. The api-version '2016-02-01' used to deploy the template does not support 'ResourceGroup' property. Please use api-version '2017-05-10' or later to deploy the template. Please see https://aka.ms/arm-template/#resources for usage details.'."
FAIL
FAIL	github.com/terraform-providers/terraform-provider-azurerm/azurerm	72.635s

But passes in this branch, containing the SDK upgrade:

$ acctests azurerm TestAccAzureRMTemplateDeployment_nestedTemplate

=== RUN   TestAccAzureRMTemplateDeployment_nestedTemplate
=== PAUSE TestAccAzureRMTemplateDeployment_nestedTemplate
=== CONT  TestAccAzureRMTemplateDeployment_nestedTemplate


--- PASS: TestAccAzureRMTemplateDeployment_nestedTemplate (978.70s)
PASS
ok  	github.com/terraform-providers/terraform-provider-azurerm/azurerm	979.175s

Fixes #2507

[katbyte]

LGTM 👍

[ghost]

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