qemu: domain: Assume 'raw' default storage format also for network storage

qemu: domain: Assume 'raw' default storage format also for network storage

Post parse callback adds the 'raw' type only for local files. Remote
files can also have backing store (even local) so we should do this also
for network backed storage.

Note that virStorageFileGetMetadata always considers files with no type
as raw so we will not accidentally traverse the backing chain and allow
unexpected files being labelled with svirt labels.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>