libxenlight: remove any uuid dependancies from xl

libxenlight: remove any uuid dependancies from xl

uuid handles in create and now create_device_model need to fill the
uuid field by client. the uuid field happens to be the exact same size
as the standard uuid (sixteen 8 bits values).

stubdom need to have a uuid when created, so using the one in
create_device_model.

this permits the client library to generate the uuid in any way it see
fits (even if it's not compliant to any standard), and simplify
installation of the libxenlight header.

xl converted from libuuid generated uuid to generated through random()
C call.  need to be fixed if anyone plan to use xl for anything
seriously apart from developing libxl.

Signed-off-by: Vincent Hanquez <vincent.hanquez@eu.citrix.com>