teamspeak-client: fix stuck build

[B4dM4n]

Motivation for this change

The teamspeak-client build gets stuck waiting for user input. When the installer gets executed via echo -e 'q\ny' | sh -xe $src, it displays the license to the user through less, which doesn't receive the q properly and stays alive.

To not modify the installer the less command will be replaced by a script that only calls cat to output the license.

Shortly after pushing this I realized there was a read before the less command in the installer, so a missing \n was all it took to fix the build.

Turns out, the first try was the correct fix and using overlays while testing is a bad idea (need to figure out how to disable them temporarily).

Fixes #69415

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip" (no depend pkgs)
• 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
• Fits CONTRIBUTING.md.

Notify maintainers

cc @nathanielbaxter

[infinisil]

How can I reproduce the failure from HEAD~1 from this PR? nix-build -A teamspeak_client works no problem.

[B4dM4n]

HEAD~1 gets stuck for me as reported in #69415 with the following ps-tree

nix-daemon --daemon
 \_ nix-daemon 31711
     \_ bash -e /nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh
         \_ sh -xe /nix/store/wkia500ys2xqb0rih7n4vnhnfy1px2h4-TeamSpeak3-Client-linux_amd64-3.3.0.run
             \_ sh -xe /nix/store/wkia500ys2xqb0rih7n4vnhnfy1px2h4-TeamSpeak3-Client-linux_amd64-3.3.0.run
             \_ less

I'm currently running:

# nix run nixpkgs.nix-info -c nix-info -m
 - system: `"x86_64-linux"`
 - host os: `Linux 5.2.13, NixOS, 19.09pre192418.e19054ab3cd (Loris)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3`
 - channels(root): `"nixos-20.03pre193829.f0fec244ca3"`
 - channels(fabian): `"nixos-19.09pre192418.e19054ab3cd"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[infinisil]

Hm weird, works for me. Anyways since this fixes it for you then I'll be happy to merge

[cleverca22]

i suspect its related to a newer nix-daemon as well, that supports pty's in the builder

#73485 will backport it to 19.09, which was forked while things where broken