builder/parallels: Create VM without hdd and then add it later

With this changeset `parallels-iso` builder will create the VM without default HDD. Instead, this disk will be created right after, during the _stepCreateDisk_

Otherwise, `--device-set` command option means that existing disk will be resized. It isn't working for OS X guests, because these disks are creating already with HFS partition inside (http://kb.parallels.com/en/113653)
So, this pull-request are fixing that.

/cc: @rickard-von-essen