VMware: optimize VM spawn by caching the vm_ref after creating VM

Commit cebcb28357131a2bf4761bbddebbedf2a7951a11 ensured that the
vm_ref was returned when the VM was created. We now cache this value
to save remote calls to the VC.

Change-Id: Ife2e64703f72a5b4f9b6f5b3cdfb63c2df5cadf7
Merge "VMware: optimize VM spawn by caching the vm_ref after creating VM"