Fix vcpu hotplug bug: get correct vcpu_avail bitmap

Fix vcpu hotplug bug: get correct vcpu_avail bitmap

Currently qemu has a bug: When maxvcpus > 64, qemu will get wrong
vcpu bitmap (s->cpus_sts[i]) since it only get bitmap from a long variable.

This patch, cooperate with another xend python patch, is to fix this bug.
This patch get hex string from xend, transfer it to correct vcpu_avail bitmap
which saved at an uint32_t array.

Signed-off-By: Liu, Jinsong <jinsong.liu@intel.com>
(This is [PATCH 2/2], the other half is in xen-unstable.hg)