workstation-ostree-installer: Switch to storing the OSTree repo in /
    
    Make the same change as was done for atomic-host-installer in
    e34c371501, and move to a bare repository inside the squashfs, avoiding
    name collisions on the Joliet filesystem.
    
    https://pagure.io/workstation-ostree-config/issue/17
    Signed-off-by: Owen W. Taylor <otaylor@fishsoup.net>