VMware: spawn refactor - phase 1 - execute_create_vm

Moves the inner function "execute_create_vm" from the spawn method
to vm_util. Additionally, return the vm_ref after VM creation so
an extra call to retrieve the vm_ref does not need to take place
after the fact.

partial blueprint vmware-spawn-refactor
Co-authored-by: Tracy Jones <tjones@vmware.com>

Change-Id: I67c3c8c14b6c01b160611cc001d51f1da29ffb24
Merge "VMware: spawn refactor - phase 1 - execute_create_vm"