When an async job is running, we sometimes need to know how it was
started to distinguish between several types of the job, e.g., post-copy
vs. normal migration. So far we added a specific bool item to
qemuDomainJobObj for such cases, which doesn't scale very well and
storing such bools in status XML would be painful so we didn't do it.

A better approach is to store the flags passed to the API which started
the async job, which can be easily stored in status XML.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>