Change /roles endpoint to include quotas, weights, reserved resources?

MESOS-4085 changes the behavior of the /roles endpoint: rather than listing all the explicitly defined roles, we will now only list those roles that have one or more registered frameworks.

As suggested by alexr in code review, this could be improved – an operator might reasonably expect to see all the roles that have

• non-default weight
• non-default quota
• non-default ACLs?
• any static or dynamically reserved resources