core: add dummy setter for graphicsInfo

This patch adds a dummy setter for VmDynamic.grahicsInfo attribute to VM and
VmDynamic classes. This is needed for serialization.

Change-Id: Ifb385db955ab9e48ad2c8a063655957e8151ec63
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>