builder/parallels: Attach ISO images to the default cdrom device

Attach the primary ISO to the default cdrom but restore it in the end.
If Parallels Tools ISO is attached it will be to a new cdrom device
which will be deleted in the end.

Related to: [mitchellh/packer#1502]
Merge pull request #2 from rickard-von-essen/remove_step_remove_devices

builder/parallels: Attach ISO images to the default cdrom device