Enhanced functions naming in tests

[sinabakh]

In tests, the function that returns the resource config is named like testResourceConfig. But it's not actually testing anything, so it may be better to be named like getTestResourceConfig.
So testAwsNatGatewayConfig would change to getTestAwsNatGatewayConfig.

[aliscott]

The Terraform Provider docs and examples seem to use the testAwsNatGatewayConfig naming - see testAccExampleResource here: https://www.terraform.io/docs/extend/testing/acceptance-tests/testcase.html. But I equally see how this could be confusing. I don't have a strong opinion so feel free to update them.

[sinabakh]

That's interesting, so now I think compatibility with the terraform source code might have its own advantages. So we can let them be as they are.