GH 1508 - Ensure Packer VMX is updated and saved

We need to ensure the VMWare process has exited before attempting to run VMX file cleanup steps, otherwise VMWare may overwrite our changes. While Packer does its best to ensure VMWare has exited, there's still a race condition on some OSs between VMWare flushing the VMX and Packer updating it. The workaround is to artifically wait 5 seconds.

When using the VMX builder its possible for the source machine to have a floppy and/or CD-ROM mounted which gets cloned to the new VM Packer spins up, but have no Packer configuration for those devices. With this change we always attempt to remove the mounted devices regardless of the Packer configuration.