VMWare: spawn refactor - phase 1 - create_virtual_disk

Several methods are repeating code for creating the virtual disk.
This refactor isolates the code for that task so it can be reused.

partial blueprint improve-vmware-disk-usage
partial blueprint vmware-spawn-refactor
Co-authored-by: Maithem <munshedm@vmware.com>
Co-authored-by: Tracy Jones <tjones@vmware.com>

Change-Id: If764340be76abbb24e1954f02b3ecb317ba143f9