Add support for service instance sharing

[jenspinney]

A new feature allowing service instances to be shared across orgs and spaces was released in cf-deployment version 1.10.0. This doc explains the very simple step required to enable this feature for your service (adding a shareable field to your service-level metadata in the catalog). Have you thought about enabling this for your service?

[cf-gitbot]

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

https://www.pivotaltracker.com/story/show/156648001

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