admin: Distribute libvirt-admin.conf
    
    Commit 48cd3dfa668e5033b02dd029c2e6de558a3c4583 introduced configuration
    file for libvirt-admin but forgot to distribute it.  Also the change
    made to libvirt.conf in commit dbecb87f94e8f1591e3c471b34ae48a7203c9cb3
    should've been removed thanks to introduction of separate config file.
    
    Signed-off-by: Martin Kletzander <mkletzan@redhat.com>