[electrum] tests: raise on RPC error with proper error message

Summary:
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
https://github.com/Electron-Cash/Electron-Cash/pull/2721/commits/0a1f39897d24092604092f48d182c50979e53e0c

Depends on D14742

Test Plan: pytest electrum/electrumabc/tests/regtest

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D14743