The prior refactoring can now be put to use. With the same domain
as the earlier commit 7b499262 (one qcow2 disk and an empty
cdrom drive):
$ virsh domstats --block foo
Domain: 'foo'
  block.count=2
  block.0.name=hda
  block.0.path=/var/lib/libvirt/images/foo.qcow2
  block.0.allocation=1309614080
  block.0.capacity=42949672960
  block.0.physical=1309671424
  block.1.name=hdc

* src/qemu/qemu_driver.c (qemuDomainGetStatsBlock): Use
qemuStorageLimitsRefresh to report offline statistics.
Signed-off-by: NEric Blake <eblake@redhat.com>