Feature request: add CLI flag to suppress yarn version and success message

[scinos]

Do you want to request a feature or report a bug?
Feature

What is the current behavior?
Yarn version and success message are always output

For example, with yarn 0.18.1, running the command yarn cache dir (in OSX) produces:

yarn cache v0.18.1
/Users/sergio/Library/Caches/Yarn
✨  Done in 0.05s.

This makes very hard to programatically capture the cache directory, for example to pack it and save it somewhere. In other words, I'd like to do cp $(yarn cache dir) /somewhere.

There are related open issues (#728, #788, #1340), but they don't cover this use case.