When restarting libvirt would previously lose the alias of the x509
certificate object. Upon unplug we would then not delete the
corresponding objects.

Restore the alias if we know it should be there.

Luckily for disks we don't support encrypted TLS environment, so there's
no need to regenerate the 'secret' alias for decryption.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>