add property VMware_Array_VIM_Object (for dvswitch, etc)

* array of vsphere objects, possibly nested
* enables dvswitch/dvportgroup resources in 
  vcenter module; has other applications 
  such as arrays of devices in VMs
* 'mapping' driven by wsdl properties from 
  rbvmomi plus annotations and hints

This PR is a companion to https://github.com/vmware/vmware-vcenter/pull/87