Improve testability by enabling VCAP_SERVICES to come from a specified location

[tillig]

In production, the standard builder.AddCloudFoundry() configuration mechanism is perfect, grabbing everything from the environment and building the information required.

However, in testing, like when building systems that need to interact with Cloud Foundry settings, it's really hard to specify different values because you have to actually set a real environment variable to get this to work. It'd be way nicer if you could provide the data somehow, at least in a testing scenario. That'd also help for local development where you're in VS on your local machine and need to test out VCAP stuff. (Working in, say, JSON config is easier than fudging launchSettings.json and having to escape quotes and such.)

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/150683792

The labels on this github issue will be updated when the story is started.

[jkonicki]

This was resolved by #17. Closing.