bottle: Fix --keep-old for Linuxbrew
bottle: Fix --keep-old for Linuxbrew

Reduce the differing cellar/prefix to a warning.

Linuxbrew/brew,maxim-belkin/brew,maxim-belkin/brew,hanxue/linuxbrew,rwhogg/brew,hanxue/linuxbrew,rwhogg/brew,Linuxbrew/brew,rwhogg/brew,hanxue/linuxbrew,Linuxbrew/brew,maxim-belkin/brew,Linuxbrew/brew