xl: move away from the use of cpumap for hard affinity

xl: move away from the use of cpumap for hard affinity

and start using the vcpu_hard_affinity array instead. This is done
as when, in a subsequent patch ("libxl/xl: make it possible to
specify soft-affinity in domain config file") we will become able
to deal with soft affinity, code can be shared.

This change also enables more advanced VCPU to PCPU (hard, for now)
affinity specification, in case a list is used, like:

      cpus = ["3-4", "2-6,^4"]

What it means is that VCPU 0 must be pinned to PCPU 3,4 and VCPU 1
to PCPUs 2,3,5,6 (before this change, cpus=[xx, yy] only supported
single values). Of course, the old (e.g., cpus=[2, 3]) syntax
continues to work.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>