Packer can't execute shell provisioner as sudo

You should override the execute_command. Example:

  "provisioners": [
    {
      "execute_command": "echo 'vagrant' | {{.Vars}} sudo -S -E sh -eux '{{.Path}}'",
      "scripts": [
        "scripts/foo.sh"
      ],
      "type": "shell"
    }
  ],