Aws spot lifecycle tests

[@calebamiles asks](https://github.com/cloudfoundry/bosh/pull/585#issuecomment-45359345):
> Additionally, since the spot instance creation fundamentally changes how a VM is created, would it be possible for you to add an additional test (in a separate PR) to the AWS lifecycle tests to reflect the additional functionality?

This PR adds:
*  simple AWS Spot lifecycle integration test