--quiet option should only silence the stdout handler

[rsyring]

We need to change CLILoader.option_process() so that --quiet only affects the stdout handler, not all logging handlers: https://github.com/level12/keg/blob/master/keg/cli.py#L335

The idea behind --quiet is that you can silence CLI output, and therefore avoid CRON email nose. However, with the current implementation, all log handlers are affected, which can keep log messages from getting upstream (i.e. to Logzio, rsyslog, etc.).