Implement model_from_config for creating a Deployment configuration object

[wallrj]

https://github.com/ClusterHQ/flocker/compare/flocker-cli-deploy-19#diff-1 outlines a function model_from_config which accepts an application_config and a deployment_config dictionary and returns a Deployment object populated with Application s DockerImages etc.

This ticket is about implementing that function and all the supporting model types. Also implementing some error checking for errors such as:

• Duplicate application names
• Links to unexposed ports
• Duplicate host ports

Then in followup tickets we can modify flocker.cli.script.DeployOptions and flocker.node.script.ChangeStateOptions to call that function and convert any validation exceptions into meaningful usage errors on the command line.

[wallrj]

This blocks https://github.com/ClusterHQ/flocker/issues/33

[wallrj]

This has been split into two parts. This ticket is about implementing the model_from_config skeleton and the parsing of application_configuration

220 is about parsing of deployment_configuration