clone_template has sane defaults for all providers

This is for smoke-testing templates on every provider, so making clone_template
as provider-agnostic as possible was needed.

Additional resulting changes:
- EC2 mgmt backend is able to deal with image names as well as AMIs, much as it does
  with instance names and IDs
- destroy_vm seemed generally useful, so it lives in utils.providers now
- minor cfme_data template changes, reflected in private yamls