builder/parallels: Rely on Cleanup functions to detach devices

Remove the redundant StepRemoveDevices and rely on the cleanup to be handled by:
* StepAttachParallelsTools.Cleanup
* StepAttachFloppy.Cleanup
* stepAttachISO.Cleanup
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.
builder/parallels: Disable default cdrom0 device and then enable it on cleanup

This is needed to make 'cdrom0' device unavailable during the ISO installation process.
It is required for some guest OS types, such as FreeBSD and OmniOS.
Merge pull request #1502 from JessThrysoee/remove_step_remove_devices

builder/parallels: Rely on Cleanup functions to detach devices