Add support for retrieving device info from SSU.

SSU is a tool for device management, used in the Mer Project (and by extension,
on Sailfish OS).

Done-with: Thomas Perl <thomas.perl@jolla.com>
Change-Id: I15a12f6adb93173b8b47d84230b18c4c41c1d522
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Reviewed-by: Lorn Potter <lorn.potter@jollamobile.com>