replace environment variable with nixpkgs directory

In this directory we generate all the files that we need to load nixpkgs.
This seems more robust than all those environment variables that may or not may be set.

pkgs/clan-cli/clan_cli/zerotier/__init__.py

@@ -9,7 +9,7 @@ from tempfile import TemporaryDirectory
 from typing import Any, Iterator, Optional
 
 from ..errors import ClanError
-from ..nix import nix_shell
+from ..nix import nix_shell, unfree_nix_shell
 
 
 def try_bind_port(port: int) -> bool:
@@ -87,7 +87,10 @@ def zerotier_controller() -> Iterator[ZerotierController]:
     controller_port = find_free_port(range(10000, 65535))
     if controller_port is None:
         raise ClanError("cannot find a free port for zerotier controller")
-    cmd = nix_shell(["bash", "zerotierone"], ["bash", "-c", "command -v zerotier-one"])
+
+    cmd = unfree_nix_shell(
+        ["bash", "zerotierone"], ["bash", "-c", "command -v zerotier-one"]
+    )
     res = subprocess.run(
         cmd,
         check=True,
@@ -102,7 +105,6 @@ def zerotier_controller() -> Iterator[ZerotierController]:
         raise ClanError(
             f"zerotier-one executable needs to come from /nix/store: {zerotier_exe}"
         )
-
     with TemporaryDirectory() as d:
         tempdir = Path(d)
         home = tempdir / "zerotier-one"