Non-revocable bursting over quota guarantees via limits.

Prior to introducing a revocable tier of allocation (see MESOS-4441), there is a notion of whether a role can burst over its quota guarantee.

We currently apply implicit limits in the following way:

No quota guarantee set: (guarantee 0, no limit)
Quota guarantee set: (guarantee G, limit G)

That is, we only allow support burst-only without guarantee and guarantee-only without burst. We do not support bursting over some non-zero guarantee: (guarantee G, limit L >= G).

The idea here is that we should make these implicit limits explicit to clarify for users the distinction between guarantees and limits, and to support bursting over the guarantee.