disable caching repo metadata
    
    all workstation based spins are failing due to packagekit causing gpg-agent
    spawning and keeping /dev/null open inside the compose environemnet.
    36389 ?        Ss     0:00 gpg-agent --homedir /tmp/tmp.XJ49JiQYpU/var/cache/PackageKit/26/metadata/updates-testing.tmp/gpgdir --use-standard-socket --daemon
    36417 ?        Ss     0:00 gpg-agent --homedir /tmp/tmp.XJ49JiQYpU/var/cache/PackageKit/26/metadata/updates.tmp/gpgdir --use-standard-socket --daemon
    we end up with process like above running. this only hit us as the urls
    pointed to stopped giving 404 errors
    
    Signed-off-by: Dennis Gilmore <dennis@ausil.us>