ALInfraRed: use better hidden function (_getRobotTypeString)

_getModelType is deprecated

Change-Id: I26256ffe4858f8947091cdd890e05c8c0865c0bf
Reviewed-on: http://gerrit.aldebaran.lan/19651
Reviewed-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>
Reviewed-by: ccollette <ccollette@aldebaran-robotics.com>
Tested-by: ccollette <ccollette@aldebaran-robotics.com>