###### Motivation for this change
Update to latest upstream version
###### Things done
* [ ] Tested using sandboxing ([nix.useSandbox](http://nixos.org/nixos/manual/options.html#opt-nix.useSandbox) on NixOS, or option `sandbox` in [`nix.conf`](http://nixos.org/nix/manual/#sec-conf-file) on non-NixOS linux)
* Built on platform(s)
* [x] NixOS
* [ ] macOS
* [ ] other Linux distributions
* [ ] Tested via one or more NixOS test(s) if existing and applicable for the change (look inside [nixos/tests](https://github.com/NixOS/nixpkgs/blob/master/nixos/tests))
* [ ] Tested compilation of all pkgs that depend on this change using `nix-shell -p nix-review --run "nix-review wip"`
* [x] Tested execution of all binary files (usually in `./result/bin/`)
* [ ] Determined the impact on package closure size (by running `nix path-info -S` before and after)
* [ ] Ensured that relevant documentation is up to date
* [x] Fits [CONTRIBUTING.md](https://github.com/NixOS/nixpkgs/blob/master/.github/CONTRIBUTING.md).
###### Notify maintainers
cc @worldofpeace @tfc @jtraue
A disabled nscd breaks nss module loading on NixOS, and systemd without
its nss modules doesn't really work either - instead of silently
disabling its nss modules if nscd is disabled, let the assertion in
nsswitch handle this.
nixos/modules/config/nsswitch.nix uses `passwdArray` for both `passwd`
and `group`, but when moving this into the systemd module in
c0995d22ee, it didn't get split
appropriately.
nixos/modules/config/nsswitch.nix uses `passwdArray` for both `passwd`
and `group`, but when moving this into the google-oslogin module in
4b71b6f8fa, it didn't get split
appropriately.
nixos/modules/config/nsswitch.nix uses `passwdArray` for both `passwd`
and `group`, but when moving this into the sss module in
edddc7c82a, it didn't get split
appropriately.
The configured mbuffer path will be called on both the source and target
system. If you use pkgs.mbuffer from the source host and the target host
does not have this exact derivation, you will get a broken pipe when
sending snapshots. This is the case when transferring to a non-NixOS
system or to a host with a different mbuffer version.
