fix migration to support portable fatties (#1935)

* load docker images directly from s9pk to ensure fatties can be loaded across platform

* don't migrate tmpdir

* init after package data transfer

* set default rsync options

backend/src/update/mod.rs

@@ -320,6 +320,7 @@ async fn sync_boot() -> Result<(), Error> {
             delete: false,
             force: false,
             ignore_existing: true,
+            exclude: Vec::new(),
         },
     )?
     .wait()