We need to store the block job state in the status XML so that we can
properly recover any data when reconnecting after startup and also in
the end to be able to do any transition of the backing chain that
happened while libvirt was not connected to the monitor.

First step is to note the name, type, state and corresponding disk into
the status XML.

We also need to make sure that a broken blockjob does not make libvirt
lose the VM, thus many of the errors just mark the job as invalid.
Later on we'll cancel all invalid jobs.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>