Move virt-login-shell into libvirt-login-shell sub-RPM
    
    Many people will not want the setuid virt-login-shell binary
    installed by default, so move it into a separate sub-RPM
    named libvirt-login-shell. This RPM is only generated if
    LXC is enabled
    
    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>