Rename method _get_object_view to get_container_view
Add 'get_list_view' method for getting a vSphere ListView ref
Add 'get_object_by_property' method for searching for an object by a property
Add 'vm_get' method for retrieving object properties of a single
VirtualMachine managed object

* New 'agent' helper method '_get_object_properties' added as well to
  simplify the process of collecting properties for single objects