Fig compatibility layer 649

TODO deal with port edge cases, e.g. just container port specified, or IP and port specified on host
See http://www.fig.sh/yml.html
Issues have been raised for this missing functionality, which is not yet supported by Flocker.

Fixes #649
Instead of adding them to the `ApplicationsFromConfigurationTests` case, I suggest we move all these `FigConfiguration` specific tests to a separate `TestCase` class.

Then add a test here which asserts that `Configuration._applications_from_configuration` will attempt to parse the supplied configuration for fig content first.