Integration tests

[arthurrichards77]

Need integration tests for each of the examples, building extra cases in current test_bridge.py and test_square.py

[arthurrichards77]

Example: add an additional test_lowbatt function to test_bridge.py in the examples/bridge folder. This function would use SITL and the SIM_BATT_VOLTAGE parameter to simulate a voltage drop and assure that the low battery safety fallback is triggered.