Use consistent "totals" across role / framework DRF.

Filed per a discussion on the mailing list:
https://lists.apache.org/thread.html/e8793049dbc706824507ad1302eb3d82105ff30fb7b6fa009b702ee4@%3Cdev.mesos.apache.org%3E

Currently, hierarchical role DRF uses the total cluster as a "total" under which to evaluate shares. However, framework DRF in a role differs in that we currently use the role's allocation as a "total" rather than the total cluster.

We should make these consistent, my inclination is to use the total cluster consistently for both DRF techniques (as that seems to be the approach taken in the literature).