JCLOUDS-649: Added image creation from pd, changed rawDisk to Optional<T>

Users can now create images from persistent disks. 

When images are made from PD the rawDisk attribute is not present. 
This changes Image.java to treat it as an Optional<RawDisk> instead. 
I just meant to remove the `System.out` line :) Seeing that in the output (without context) might not provide any value when running the entire test suite?