vl: Fix to create migration object before block backends again
Recent commit
cda4aa9a5a0 moved block backend creation before machine
property evaluation. This broke qemu-iotests 055. Turns out we need
to create the migration object before block backends, so block
backends can add migration blockers. Fix by calling
migration_object_init() earlier, right before configure_blockdev().
Fixes: cda4aa9a5a08777cf13e164c0543bd4888b8adce
Reported-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>