When piping stdout, output can be interlaced with status messages on stderr

[hyfen]

When running something like `$ chronicle-etl -e shell | grep "foo", we often get this sort of race condition:

result 
result
Completed job in 2.207684 secs
  Status:	Success
  Completed:	113
result
result

Options to fix this:

• detect when stdout is piped (and actually being used!) and don't print a final status message
• print status message before running loader.finish (but this might print "success" even if the loader then goes on to fail)
• adding a sleep N before the status message (hacky)