Option to clear cache

[techtonik]

It is not clear if --no-cache-dir frees the disk space or not. It will be useful to have an option that can reset current cache.

[rbtcollins]

How about a way to query where the cache is? Then you can rm -rf it yourself, and we get two things for one change.

[techtonik]

Not sure. Too much micromanagement is bothersome. I don't see why I would need to know where the query cache is, and how to reuse that info from command line to remove cache in cross-platform way.

[xavfernandez]

#3146 could help and needs feedback :)

[techtonik]

Does pip report about cache usage to user by default? If yes, then that info should mention how to disable cache.

[pradyunsg]

Closing in favour of #4685.