CONFIG: Use default config when none provided
    
    This patch makes SSSD possibly useful "out of the box" by allowing
    packagers to provide a default config file located in $LIBDIR/sssd/conf
    that will be copied by the monitor to /etc/sssd if no file already
    exists in that location. This will make it possible to have SSSD set up
    to have distribution-specific default configuration, such as enabling
    the proxy provider to cache /etc/passwd (such as in the provided
    example in this patch).
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>