Tests: Bluetooth: Mesh: add BSim tests for Private Beacons

This set tests if Private Beacons are advertised properly, with address
changed for every beacon and Random value changing appropriately
regarding the scenario (IV Update, Key Refresh, advertisements on device
with friendship support) and Random Interval state.

All tests contain two devices: tx advertises Private Beacon (has Private
Beacon Server in composition) and rx sets Private Beacon state on tx
device (has Private Beacon Client). On rx device, scan callback is
registered to monitor Private Beacon advertisements.

Signed-off-by: Krzysztof Kopyściński <krzysztof.kopyscinski@codecoup.pl>