Feature request: be able to override logdev after creation

[perlun]

This could be a useful feature, especially in specs where you often want to silence the logging.

I looked briefly at the code in https://github.com/chef/mixlib-log/blob/master/lib/mixlib/log/logger.rb, and it seems to be pretty simple; it's just an attr_accessor or attr_writer that would need to be added.

Are you against it for philosophical reasons, or would you consider a PR that adds this? Or is there another suggested way to change the output device of a logger after it has been created?