migrateStatus() progress report

The percentage is based on libvirt dataTotal and dataRemaining
fields of the virDomainJobInfo struct

Signed-off-by: Peter V. Saveliev <peet@redhat.com>
Change-Id: I3ff00e85c88e865cd81697d427d6bd5473e0f79e
Reviewed-on: http://gerrit.ovirt.org/6824
Reviewed-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>