manifest: add attr
    
    In commit 7d50906, we dropped the 'glusterfs-fuse' package (among
    other things) which caused the 'attr' package to drop out as well.
    
    The inclusion of the 'attr' package would provide consistency with
    RHEL + CentOS and would also provide the 'getfattr' utility which is
    used by some of the 'atomic-host-tests'.