dvswitch, dvportgroup resources

* create, manage, delete vmware distributed virtual switch
* create, manage, delete distributed virtual portgroups 
* requires VMware_Array_VIM_Objects property from module vmware_lib
* coverage is incomplete; example missing properties: multiple
  uplink portgroups, vmDirectPath, vendorSpecificConfig,
  pvlan, ipfix, vspan, etc.
    
Also, in support:
* added technique for abstract types to handle conflicting
      property keys in concrete subtypes with ABSTRACT2, :node_types