Improve error messaging in integration testing

[maylee]

Some ideas/discussion:

• One enduser improvement could be to turn off non-useful error messages
• Some kind of helpful action should be suggested in an error message
• Sysadmin logging with no error messages (set up new logger and there will be at least some improvement at the debug level)
• Switch all logging to new Twisted logging library
• Improve non-Foolscap logging (use Eliot-based logging?)