Motivation for this change

lxd networking is broken in nixos. On initial setup with lxd init it works because when running lxd directly sh is in PATH. Running lxd network edit afterwards fails.
The problem is sh is not in PATH and lxd is not using /bin/sh as can be seen here https://github.com/lxc/lxd/blob/master/lxd/iptables.go#L97.

Things done

In this PR I add /bin/ to the PATH available for the lxd wrapper.
Added bash to makeBinPath to provide sh executable t lxd.

• 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 nox --run "nox-review wip"
• 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)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.