include distro tag in VERSION file
    
    NVR: docker-1.7.0-6.git56481a3
    
    - This will let 'docker version' display the distro version as well which is
    helpful in finding out if the docker rpm is distro supplied or provided by
    upstream docker
    
    Signed-off-by: Lokesh Mandvekar <lsm5@fedoraproject.org>