Fix upload

Current app build failed with following error:

$ rsync -e "ssh -oStrictHostKeyChecking=no -i $ARCHIVE_SECRET_FILE" -aP ~/.cache/flatdeb/ostree-repo/. "$upload_host:$UPLOAD_ROOT"
sending incremental file list
rsync: change_dir "/root/.cache/flatdeb/ostree-repo" failed: No such file or directory (2)

This commit create a temporary repo directory used by flatpak-builder.
Set correct rights so the repository is accessible after upload.

Signed-off-by: Frédéric Danis frederic.danis@collabora.com