core, engine: Get CD interface through osinfo

This patch allows the specification of the bus used to connect the
virtual CD-ROM (currently either IDE or SCSI). A property to indicate
this was created in the osinfo and the necessary modifications were
made in the VmInfoBuilder class.

Change-Id: I579fdcc0b6bdf7d23bd60efc33fbc4bad1595324
Signed-off-by: Vitor de Lima <vitor.lima@eldorado.org.br>