utils: Add a unique ADUGroup tag for created Azure IoT device

Each Azure Device Update (ADU) update is deployed to all IoT devices
in a given ADUGroup. In the CI of open-iot-sdk and total-solutions,
each dynamically created IoT device is tested independently, so its
ADUGroup must also be unique. For simplicity we set ADUGroup to the
Device Id.

Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>