Improve the way we wait for commands in driver (#3398)
Improve the way we wait for commands in driver (#3398)

* Improve the way we wait for commands in driver
- avoid leaving orphaned command subprocesses
- don't let CTRL+C kill the driver, forward it instead

* Polish module imports in driver
p4lang/p4c,p4lang/p4c,p4lang/p4c,p4lang/p4c,p4lang/p4c