Support for VMware vCenter in roxy branch

OpenStack Compute supports the VMware vSphere. This patch brings support for vmwareapi.VMwareVCDriver.

With this driver that lets nova-compute communicate with a VMware vCenter server managing a cluster of ESX hosts. With this driver and access to shared storage, advanced vSphere features like vMotion, High Availability, and Dynamic Resource Scheduling (DRS) are available. With this driver, one nova-compute service is run per vCenter cluster.