Split rpm-build-libs to one more subpackage rpm-sign-libs
    
    This is the only package in default buildroot pulling in gnupg2 which
    pulls gnutls, libgcrypt, nettle…
    
    Acked-by: Panu Matilainen <pmatilai@redhat.com>
    Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>