add service_guid and service_url to service instance entity

[jeffpak]

Thanks for contributing to the cloud_controller_ng. To speed up the process of reviewing your pull request please provide us with:

• A short explanation of the proposed change:

Allow users access to a service instance's service offering without having to go through the service plans endpoint.

• An explanation of the use cases your change solves

1. You no longer have to go through an additional endpoint to hit a service instance's service offering.
2. If a service instance's plan is private, you can more easily find its service offering through one direct endpoint.

• I have viewed signed and have submitted the Contributor License Agreement
• I have made this pull request to the master branch
• I have run all the unit tests using bundle exec rake
• I have run CF Acceptance Tests on bosh lite
• This lets users access a service instance's service offering
  without having to go through its service plan. This does not
  introduce a database migration.

[#130772287]

[cfdreddbot]

Hey jeffpak!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you and the commit authors have already signed the CLA.

[cf-gitbot]

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

https://www.pivotaltracker.com/story/show/132867779

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

[jeffpak]

This is my output from the command: