Consider turning off auto-optimise-store on Linux too

[Hoverbear]

Refer to #542 (review)

[sbp]

In issue #879 I describe having problems setting auto-optimise-store to false with the installer. I'm turning off auto-optimise-store because I'm installing Nix in a container, and when auto-optimise-store is true during the layer build process, the hard links get messed up and garbage collection no longer works in the resulting container. This is another argument for a subset of the suggestion in this thread, i.e. for Linux OCI containers at least, that auto-optimise-store should be false.