migrate testing framework to terraform-plugin-testing

[fantapop]

Previously, the terraform provider utilized the sdkv2 framework. In order to stay up to date with testing framework improvements we upgrade to the new terraform-plugin-testing framework following these instructions:

https://developer.hashicorp.com/terraform/plugin/testing/migrating

The change that instigated this upgrade is that the id field is no longer required in the new framework. During development of the role_grant_resource an ID was not used because the ccapi does not provide an ID for it. Rather than work around this using a synthetic ID, we upgrade.

Commit checklist

• [x] Changelog
• [x] Doc gen (make generate)
• [x] Integration test(s)
• [ ] Acceptance test(s)
• [ ] Example(s)

[fantapop]

@carloruiz / @andy-kimball as recent contributors to the terraform provider, I've added you two here as reviewers.

[fantapop]

The changes are separated into 2 commits, one with all the vendor changes. Don't let the 1600+ file counts scare you since its mostly vendor.