glpi/imaging: Fixing no Mac address found

For imaging registration, always return MAC address
imaging/glpi: Add network uuid for imaging registration

network uuid is mandatory for imaging registration
imaging: [fix] register a computer with PXE on GLPI mode

Bug description:
A traceback received in pulse2-package-server.log durring the attempt
of generate a boot menu for a new machine.
imaging: Fixing a traceback when registering computer

If an imaging server is set on an entity, and if a computer is member
of a child of this entity, bootmenu cannot be set. Pulse set menu by
searching with parent entity instead of child entity.

This commit fix it.