Add reporting URL to credentials

[denicaM]

We need reporting URL in credentials section Broker returns.

This will save documentation efforts from integrator side. For resource provider this will allow reading the URL in more standardized form. See PR #142 from cf-abacus-broker

* The issue originally was reported in the deprecated cf-abacus-broker repo: cloudfoundry-attic/cf-abacus-broker#143

[cf-gitbot]

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

https://www.pivotaltracker.com/story/show/155619851

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