dockerTools.fakeNss: add /etc/nsswitch.conf (#134958)
dockerTools.fakeNss: add /etc/nsswitch.conf (#134958)

Apparently, a non-existent nsswitch.conf causes a very misleading host
resolution, differing from the defaults people are used to.

According to
https://github.com/golang/go/issues/22846#issuecomment-346377144, glibc
says the default is "dns [!UNAVAIL=return] files".

This means, `/etc/hosts` isn't really honored, causing all sorts of
unexpected behaviour.

Let's prevent this, and first ask `/etc/hosts` before querying DNS, like
we do on NixOS too.
NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs