Introduce new enum BlockdevOptionsArchipelago.

@volume:              #Name of the Archipelago volume image

@mport:               #'mport' is the port number on which mapperd is
                      listening. This is optional and if not specified,
                      QEMU will make Archipelago to use the default port.

@vport:               #'vport' is the port number on which vlmcd is
                      listening. This is optional and if not specified,
                      QEMU will make Archipelago to use the default port.

@segment:             #optional The name of the shared memory segment
                      Archipelago stack is using. This is optional
                      and if not specified, QEMU will make Archipelago
                      use the default value, 'archipelago'.

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>