Implement Stack Class

[robparrott]

Currently this is a glaringly lacking feature/capability.

We need to implement a Stack class that encompasses a "Scenario" (Blueprint + params [ + context?] ) but that is serializable and trackable. This will let us more easily implement nepho stack list and other operations, and will enable multiple stacks per blueprint (a constraint right now.

Upon successful execution of provider.create(), the provider (or scenario?) should return a Stack object, and then save it. These saved stack objects could be YAML files stored within ~/.nepho/local/, one per stack? A lookup for all stack of a given provider, or cloudlet, or cloudlet+blueprint should be implemented in the ResourceManager helper class, so that implementation changed underneath are transparent to the rest of the codebase.

Stack should have fields:

• s.id
• s.provider
• s.blueprint
• s.params
• s.context?

and methods

• s.status()
• s.access()
• s.destroy()

Stack will use the provider class in the backend to do these actions, so that they are pluggable.

ResourceManager needs new method:

• rm.find_stacks( provider=None, cloudlet=None, blueprint=None)

which returns a list of Stack objects.

StackController class will need to be modified to use "Stack" objects instead of provider in the destroy(), status() and list() methods (and any other that come down the road).