libify util.py, use it directly from test.py

Use the functions in util.py directly instead of forking sub-processes.
This is a change in behaviour: if an OK-packet is missing, test.py will
now hang. Before, missing OKs were just ignored. Fix for hang pending.

Also, there's a required change in sleep times.
Check for OK packets

For each message sent, an OK packet is expected within 3 seconds
Test send/receive in both directions
Split test verbose mode into two: test and nodes

This add a -V flag to pass BE_VERBOSE=1 env to nodes, independently of
test verbose mode -v