VMware: fix list_instances for multi-node driver

VMwareVCDriver should only list instances in the nodes managed by
it. Currently, it uses the an implementation that lists instances
in the vCenter server inventory even if they are not in the nodes
managed by the driver.

Closes-bug: #1272286
Change-Id: I56c81a759eacc8c595e97ac5ca372834b675ebff
Merge "VMware: fix list_instances for multi-node driver"