JCLOUDS-529: fix aws-ec2 cleanupIncidentalResources

- Some users get a `DependencyVioloation`, rather than `InvalidGroup.InUse`, when attempting to delete the security group. This caused `cleanupIncidentalResources` to propagate an exception.
- Fixes it by converting this to an `IllegalStateException` (in same way as is done for `InUse`)
- Adds tests (using `MockWebServer`) for happy-path and for failing to delete the security group with each of `InUse` and `DependencyViolation` responses.