* feat(tests) Add Terraform testing to support Cross-account discovery
**Problem**
* To support cross-account DHC discovery, we need to add terraform configurations and tests to test against live AWS data.
* However, there was nothing in place to support any AssumeRole testing, irrespective of cross-account.
**Solution**
* Added a new terraform file, iam_assume_role.tf, to contain the new terraform configurations for single-account AssumeRole and cross-role
* Added a second terraform file, iam_cross_account.tf, to contain the new terraform configurations for cross-account
* Refactored how the tests are organized. The previous static test cases used a system where a separate function was created for each test. This was moved to a dedicated file, e2e_host_static_test.go.
* For AssumeRole tests (single account, cross role, and cross account), this system wasn't ideal since there are so many test cases and they are all extremely similar. A table driven system was better that passed in a set of variables to shared test helpers. A dedicated file, e2e_host_assumerole_test.go, was created to contain the testing infrastructure for AssumeRole tests.
* e2e_host_test.go remains the main test runner that then calls e2e_host_assumerole_test.go and e2e_host_static_test.go
* The terraform tests work by setting environment variables for the AWS account that you want to configure the terraform for. The existing setup worked for single-account and cross-role. However, to support cross-account, support had to be added for a second set of credentials. The second set of environment variables can now be set with the TARGET_ prefix. Some configuration in testing.go had to be added to support creating/destroying multiple terraform setups.
**Testing**
* The single account tests pass as expected. However, a bug was discovered during this process that will be addressed later.
* The cross-role and cross-account tests failed as expected because this featured has not yet been delivered.
* It was noticed that some of the existing static tests were flaky. The problem and fix were identified and will be addressed later.
Matt Romanelli
11c036e28b