VMware: Add fake.create_vm()

Add a utility function for creating VMs in tests. Based on the
existing FakeVim._create_vm function which implements CreateVM_Task.
FakeVim._create_vm is refactored to call create_vm.

Change-Id: I4949408420704cd7e6dd4fc11226472362422a93
Merge "VMware: Add fake.create_vm()"