This makes it easier to diagnose RPC errors.
Without raising on timeout error, poll_for_answer would just continue execution, now it will fail the test if a response is not received.
Also run the electrum-abc process in verbose mode for additional debugging info on stdout, and add an additional debugging/error message if the result == PACKAGE_VERSION assertion fails (which misteriously happens occasionnaly on our CI infra)
This is a partial backport of electroncash#2721
Depends on D14742