Initial work to implement additional disk support in the vmware-iso builder

* Matches the syntax from mitchellh/packer#703
* Creates disk(s), adds them to the vmx template, and runs compact at the end
Formatting cleanups from `go fmt`
Fix vmware compact_disk step when there are no additional disks
Merge branch 'master' into AdditionalDisksForVMwareISO

Conflicts:
	builder/vmware/iso/builder.go
Merge branch 'AdditionalDisksForVMwareISO' into winrm-merged