builder/parallels: Added driver method 'DeviceAddCdRom'
builder/parallels: Attach ISO images to the separate cdrom device

For each ISO image the individual cdrom device will be added to the VM. During the cleanup these devices will be deleted.
It makes attach steps more clear - there is no doubt what is the name of the device.

Related to: [mitchellh/packer#1502]
builder/parallels: Added setting the boot order

CD/DVD drive with installation ISO should be exactly the 2nd device in the VM boot order.
This ensures that VM will boot from this ISO at the first boot time only.
Merge pull request #1 from legal90/remove_step_remove_devices

Attach ISO images to the separate cdrom device