Adding SSD support

Adds the ability to specify a disk type when creating a disk.

Impact: users are able to use SSDs. 
Instead of having the `jsonBinder` variable and exposing this public method, would it make sense to directly extend the `BindToJsonPayload` class?

This way we can get rid of this variable and public setter, and we should only have to implement the method that accepts the `Map<String, Object>`; the other one could be removed, as the `BindToJsonPayload` already implements it the right way.