Add ability to create eager-zeroed disks from thin templates

[ShimShtein]

Right now, every disk that is inherited from template, would remain thin.

The code missing relocation spec that will set the disk to flat, if the configuration is different from what was specified in the template.

[ShimShtein]

It's worth looking at VMWare API for better implementation, but I found a workaround: in order to make thick disks from thin templates, one must set options[:transform] to flat. The problem is that it's not per-disk setting, which means all disk will be thin or thick, based on this option.