Add models for cloud orchestration

This PR is split from original PR #333  (to be discarded). It focus only on the models for orchestrations. 
The master PR #523 covers the design and progress of the support for orchestration including AWS CloudFormation and OpenStack Heat.
![orchestration](https://cloud.githubusercontent.com/assets/7047579/4719534/6144c4e0-592a-11e4-9dc1-7d882f00f947.png)

I can't think of good examples, but one option is to doc the method into existence, without actually defining it:

``` ruby
# :method: raw_delete_stack
```

Alternatively, a bare `raise NotImplementedError` is generally held to mean "the method that raised this is abstract" without needing further clarification... even though `NotImplementedError` is documented as meaning it's not implemented *by the VM*.