Reset LV status when unlinking LV from VG

When LV is unlinked, we want to catch problem in vg_validate,
that LV has changed.

i.e. catch LV has been removed and is no long thin_pool while still
being referenced by some thin volume.

lib/metadata/lv_manip.c

@@ -3028,6 +3028,8 @@ int unlink_lv_from_vg(struct logical_volume *lv)
 
 	dm_list_del(&lvl->list);
 
+	lv->status = 0;   /* Reset */
+
 	return 1;
 }