Fix failure of AUM in case of upgrading with override-commit

In case if 'origin' file contain some transient state the online upgrade fails with error: "OSTree:ERROR:src/libostree/ostree-repo-pull.c:1823:scan_commit_object: assertion failed: (ref)"

In case of Apertis the "override-commit" is heavily used for test purposes. Have to cleanup the origin prior to pulling the upgrade.

Signed-off-by: Denis Pynkin denis.pynkin@collabora.com