[utils] use DBus and ssud to get device UID

Our SsuDeviceInfo::deviceUid() call doesn't always return a value
consistent with what 'ssu status' gives. Let's do it the same way ssu
client does, contacting ssud on DBus.

The daemon eventually calls SsuDeviceInfo().deviceUid() as well; why the
who values differ is beyond my comprehension.
Incremented version