libvirt: Introduce protected key mgmt ops

libvirt: Introduce protected key mgmt ops

Two new domain configuration XML elements are added to enable/disable
the protected key management operations for a guest:

    <domain>
      ...
      <keywrap>
        <cipher name='aes|dea' state='on|off'/>
      </keywrap>
      ...
    </domain>

Signed-off-by: Tony Krowiak <akrowiak@linux.vnet.ibm.com>
Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
Signed-off-by: Daniel Hansel <daniel.hansel@linux.vnet.ibm.com>
Reviewed-by: Boris Fiuczynski <fiuczy@linux.vnet.ibm.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>