Move to a four-endpoint topology.
Remove the 'handle_config_error' function and create 'get_eth_id'.
Remove the requirement to have the binary file in the config file.
Enable checks that audio streams are not lost at any point.

Redundant connects caused the audio to be disconnected and reconnected (BUG 15150).
Test infrastructure adds a clock master in the case of loops.
Tidy up the test script main.