Use different clients for SSO and backend access

[denicaM]

Currently there is only one UAA client used in the dashboard.

From my point of view it makes sense to use one client for the SSO and another for accessing the backend(provisioning). This will lead to better separation of concerns and will allow us to use the automatic registration of the dashboard_client which we've discarded with 45d36ac.

* The issue originally was reported in the deprecated cf-abacus-broker repo: cloudfoundry-attic/cf-abacus-broker#37

[cf-gitbot]

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

https://www.pivotaltracker.com/story/show/155619592

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