Basic Plan Bind & Unbind

[jasonmimick]

Ensure the broker can successfully bind and unbind a Cloud Foundry app with an instance of the Basic Plan.

[jasonmimick]

Maps to:

• Use case 9: As a user, I should be able to bind my app to a existing service instance   (Sprint 2)
• Use case 12: As a user, I should be able to create new Atlas credentials by leveraging the cf create-service-key and pass in custom roles (Spring 2)

[jasonmimick]

Existing and desired VCAP_SERVICES connection string data see #4

We will research the feasibility for an enhancement in the design to support a way to convert the Atlas API connection string https://github.com/mongodb/go-client-mongodb-atlas/blob/master/mongodbatlas/clusters.go#L81 into any desired format.

[jasonmimick]

Update specs here: https://github.com/jasonmimick/atlas-osb/blob/master/docs/custom-plans.md#bind--unbind