download: change /mnt/koji/compose mount on download servers
    
    Turns out odcs uses links to /mnt/koji for all it's packages.
    This means we need to have /mnt/koji on the download servers for the
    odcs composes to work right. Additionally, somehow /srv/odcs was mode
    770 and apache couldn't read it. I changed it to 775, will need to make
    sure this doesn't cause any issues.
    
    Signed-off-by: Kevin Fenzi <kevin@scrye.com>