The worker threads could exit prematurely if they finished processing
all items while the main thread was still adding items. In particular,
this caused hanging nix-store --serve processes in the build farm.

Also, process items from the main thread.

release-common: Fix busybox builtins (busybox >= 1.27)

See https://github.com/NixOS/nixpkgs/pull/28261

fixing bashisms in test code

This fixed the build on ubuntu/debian, where dash is the sh.

Fix tests

I got sick of trying to find the failures in the sea of debug output, so
we now:
- Hide test output unless it fails
- Sprinkle in some simple color
- Pad results for a more tabular look

If Nix is getting a more friendly user interface, we might as well get
a friendlier developer interface, right? :)

`nix copy` no longer accepts a `--recursive` argument

Otherwise Ctrl-C doesn't work.

This debug command prints a store derivation in JSON format. For
example:

  $ nix show-derivation nixpkgs.hello
  {
    "/nix/store/ayjwpwwiyy04nh9z71rsdgd3q7bra7ch-hello-2.10.drv": {
      "outputs": {
        "out": {
          "path": "/nix/store/w5w4v29ql0qwqhczkdxs94ix2lh7ibgs-hello-2.10"
        }
      },
      "inputSrcs": [
        "/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh"
      ],
      "inputDrvs": {
        "/nix/store/13839aqdf6x4k3b785rw5f2l7857l6y3-bash-4.4-p12.drv": [
          "out"
        ],
        "/nix/store/vgdx7fdc7d4iirmnwj2py1nrvr5qwzj7-hello-2.10.tar.gz.drv": [
          "out"
        ],
        "/nix/store/x3kkd0vsqfflbvwf1055l9mr39bg0ms0-stdenv.drv": [
          "out"
        ]
      },
      "platform": "x86_64-linux",
      "builder": "/nix/store/qp5fw57d38bd1n07ss4zxh88zg67c3vg-bash-4.4-p12/bin/bash",
      "args": [
        "-e",
        "/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh"
      ],
      "env": {
        "buildInputs": "",
        "builder": "/nix/store/qp5fw57d38bd1n07ss4zxh88zg67c3vg-bash-4.4-p12/bin/bash",
        "configureFlags": "",
        "doCheck": "1",
        "name": "hello-2.10",
        "nativeBuildInputs": "",
        "out": "/nix/store/w5w4v29ql0qwqhczkdxs94ix2lh7ibgs-hello-2.10",
        "propagatedBuildInputs": "",
        "propagatedNativeBuildInputs": "",
        "src": "/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz",
        "stdenv": "/nix/store/6zngq1rdh0ans9qyckqimqibgnlvlfrm-stdenv",
        "system": "x86_64-linux"
      }
    }
  }

This removes the need for pp-aterm.

Fixes #1563.

Fixes #1568.

These have a GCC (4.9) that is too old.

https://hydra.nixos.org/eval/1391740

This is a hack to make hydra-queue-runner free its temproots
periodically, thereby ensuring that garbage collection of the
corresponding paths is not blocked until the queue runner is
restarted.

It would be better if temproots could be released earlier than at
process exit. I started working on a RAII object returned by functions
like addToStore() that releases temproots. However, this would be a
pretty massive change so I gave up on it for now.

For example,

  $ nix-store -q --roots /nix/store/7phd2sav7068nivgvmj2vpm3v47fd27l-patchelf-0.8pre845_0315148
  {temp:1}

denotes that the path is only being kept alive by a temporary root
(i.e. /nix/var/nix/temproots/). Similarly,

  $ nix-store --gc --print-roots
  ...
  {memory:9} -> /nix/store/094gpjn9f15ip17wzxhma4r51nvsj17p-curl-7.53.1

shows that curl is being used by some process.

docker: update to Nix 1.11.14

For example, without --all:

  $ nix why-depends nixpkgs.nixUnstable nixpkgs.libssh2
  /nix/store/s9n5gvj2l49b4n19nz6xl832654nf7n7-nix-1.12pre5511_c94f3d55
  └───lib/libnixstore.so: …/lib:/nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0/lib…
      => /nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0
      └───lib/libcurl.la: …ib -L/nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0/l…
          => /nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0

but with --all:

  $ nix why-depends -a nixpkgs.nixUnstable nixpkgs.libssh2
  /nix/store/s9n5gvj2l49b4n19nz6xl832654nf7n7-nix-1.12pre5511_c94f3d55
  ├───lib/libnixstore.so: …/lib:/nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0/lib…
  │   => /nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0
  │   └───lib/libcurl.la: …ib -L/nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0/l…
  │       lib/libcurl.so.4.4.0: …/lib:/nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0/l…
  │       => /nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0
  └───lib/libnixstore.so: …/lib:/nix/store/bx2i9vi76lps6w9rr73fxf6my31s4dg5-aws-sdk-cpp-1.0…
      => /nix/store/bx2i9vi76lps6w9rr73fxf6my31s4dg5-aws-sdk-cpp-1.0.153
      └───lib/libaws-cpp-sdk-core.so: …e.so./nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0/lib…
          lib/libaws-cpp-sdk-s3.so: …/lib:/nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0/lib…
          => /nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0

- Use the latest Nix version 1.11.14.

- Attempts to download the Nix installation tarball from http://nixos.org
  redirect to https these days, which wget doesn't support unless OpenSSL is
  available.

- Use addgroup and adduser commands to create the Nix build users.

- Link the Nix profile script into /etc/profile.d, where it's run
  automatically.

- Dropped installation of bash and tar. Neither tool is essential for running
  Nix.

Use the command "docker build -t nix . && docker run -it --rm nix sh -"
to build and run the Nix docker container.

This command shows why a package has another package in its runtime
closure. For example, to see why VLC has libdrm.dev in its closure:

  $ nix why-depends nixpkgs.vlc nixpkgs.libdrm.dev
  /nix/store/g901z9pcj0n5yy5n6ykxk3qm4ina1d6z-vlc-2.2.5.1:
    lib/libvlccore.so.8.0.0: …nfig:/nix/store/405lmx6jl8lp0ad1vrr6j498chrqhz8g-libdrm-2.4.75-d…

  /nix/store/s3nm7kd8hlcg0facn2q1ff2n7wrwdi2l-mesa-noglu-17.0.7-dev:
    nix-support/propagated-native-build-inputs: …-dev /nix/store/405lmx6jl8lp0ad1vrr6j498chrqhz8g-libdrm-2.4.75-d…

Thus, VLC's lib/libvlccore.so.8.0.0 as well as mesa-noglu's
nix-support/propagated-native-build-inputs cause the dependency.

Also some refactoring.

I don't remember what the reasoning was here, but security is provided
by the signatures, not by whether the hash is provided by the other
store.

In particular, process() won't return as long as there are active
items. This prevents work item lambdas from referring to stack frames
that no longer exist.

Since we may use a dedicated file descriptor in the future, this
allows us to change it. So builders can do

  if [[ -n $NIX_LOG_FD ]]; then
    echo "@nix { message... }" >&$NIX_LOG_FD
  fi