hspace computes the NPU (normalised CPU units) via the
(used|pool|avail) VCPU divided by the (currently cluster-wide) max
vcpu_ratio.

However, in the future we'll have variable vcpu_ratios, so we can't
the calculation as such. We temporarily change to computing the
average vcpu_ratio across the cluster, however long-term this needs to
be improved, as ∑ (Vi/Pi) ≠ ∑ Vi / ∑ Pi. In the meantime we implement
this patch to remove the use of a global mcpu variable.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>