(QENG-1209) scp in debug output shows far too much output

- move detailed output into a new log level called 'trace', could still
  be useful for tracking networking failures - but will be disabled by
  default
- add ability to flip on/off quiet output to logging
Merge pull request #452 from anodelman/maint

(QENG-1209) scp in debug output shows far too much output