Albatross policy management

[hannesm]

An administrator should be able to

• see and
• adjust policies (Vmm_core.Policy.t) for each user.

[hannesm]

I guess a first step would be to display such a policy..

  type t = {
    vms : int;
    cpuids : IS.t;
    memory : int;
    block : int option;
    bridges : String_set.t;
  }

Which means: the number of unikernels/vms that are allowed to be executed at the same time. Which CPUids are accessible (a set of numbers, each unikernel is sticky on a single CPU), the amount of memory in MB, the amount of block storage in MB, and a set of names of bridges that are available.

The CPUids is a bit weird, I guess we could as well say "how many CPUs" -- since someone may have 10 unikernels run on a single CPU, and then another one that has a high load on a different one. But exposing the IDs to a client isn't necessarily what we want to do -- but that's likely for a later step, that mollymawk has some heuristics which CPU to pick ;)

[hannesm]

done in #57