Issue-820: 'ticketId cannot be null' for a Facebook authentication

Fixed the problem by adding the ticket granting ticket in flow scope. Updated the test accordingly.
I only find four references of these methods:
- request scope: https://github.com/Jasig/cas/blob/master/cas-server-core/src/main/java/org/jasig/cas/web/flow/AbstractNonInteractiveCredentialsAction.java#L103
- flow scope: https://github.com/Jasig/cas/blob/master/cas-server-webapp-support/src/main/java/org/jasig/cas/web/flow/AuthenticationViaFormAction.java#L198
- flow scope: https://github.com/Jasig/cas/blob/master/cas-server-webapp-support/src/main/java/org/jasig/cas/web/flow/InitialFlowSetupAction.java#L86
- this one.

It could be a good simplification. I don't think there would be any side effect. I captured this idea here: https://github.com/Jasig/cas/issues/825.