[WSL] Don't allow root nix instalation on WSL (#709)

## Summary

This shows an error is user tries to install nix on WSL as root. cc:
@Lagoja

## How was it tested?

Untested

internal/boxcli/setup.go

@@ -6,7 +6,6 @@ package boxcli
 import (
 	"fmt"
 	"os"
-	"os/user"
 
 	"github.com/fatih/color"
 	"github.com/mattn/go-isatty"
@@ -93,7 +92,7 @@ func ensureNixInstalled(cmd *cobra.Command, args []string) error {
 
 func nixDaemonFlagVal(cmd *cobra.Command) *bool {
 	if !cmd.Flags().Changed(nixDaemonFlag) {
-		if u, err := user.Current(); err == nil && u.Uid == "0" {
+		if os.Geteuid() == 0 {
 			ux.Fwarning(
 				cmd.ErrOrStderr(),
 				"Running as root. Installing Nix in multi-user mode.\n",

internal/nix/install.go

@@ -11,13 +11,18 @@ import (
 
 	"github.com/fatih/color"
 	"github.com/pkg/errors"
+	"go.jetpack.io/devbox/internal/boxcli/usererr"
+	"go.jetpack.io/devbox/internal/telemetry"
 )
 
 const rootError = "warning: installing Nix as root is not supported by this script!"
 
 // Install runs the install script for Nix. daemon has 3 states
 // nil is unset. false is --no-daemon. true is --daemon.
 func Install(writer io.Writer, daemon *bool) error {
+	if isRoot() && telemetry.IsWSL() {
+		return usererr.New("Nix cannot be installed as root on WSL. Please run as a normal user with sudo access.")
+	}
 	r, w, err := os.Pipe()
 	if err != nil {
 		return errors.WithStack(err)
@@ -79,3 +84,7 @@ func DirExists() bool {
 	_, err := os.Stat("/nix")
 	return err == nil
 }
+
+func isRoot() bool {
+	return os.Geteuid() == 0
+}

internal/telemetry/telemetry.go

@@ -55,3 +55,7 @@ func OS() string {
 
 	return os
 }
+
+func IsWSL() bool {
+	return OS() == "wsl"
+}