This should be completely backwards compatible. It allows the '-f' part
of the nix-env command to be configured. This greatly eases using
nixos-container as part of development where several nixpkgs
repositories might be tested at the same time.
My earlier commit to have `nixos-container destroy` use `kill` broke
the `container-imperative` test, see[1]. As suggested by @aszlig,
`machinectl terminate` doesn't have that problem, and is the command
that should have been used to begin with rather then `kill`.
1| 60c6c7bc9a (commitcomment-18478032)
Using 'machinectl kill' is much faster then gracefully stopping the
container.
In the case of 'destroy', since we're destroying it anyway, there's no
reason to do a graceful shutdown.
This moves nixos-containers into its own package so that it can be
relied upon by other packages/systems. This should make development
using dynamic containers much easier.
