Add delete retries

[optik-aper]

Description

The tests were failing because of the VPC not being fully detached from a load balancer before the delete command was issued. Essentially, the load balancers are too slow to shutdown and delete so the VPC remains in an attached state when the delete command is sent by Terraform. This PR does two things to help in the case that a VPC is attached to a load balancer:

• When deleting, issue an update against a load balancer to detach the VPC
• Add a retry on the VPC resource to check the error returned from the API and re-issue the delete command after a short wait.

Related Issues

Closes #355
A similar solution might work for #348

Checklist:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you linted your code locally prior to submission?
• Have you successfully ran tests with your changes locally?

[mondragonfx]

lgtm