Add a method for sanity checking of the client message
Remove left-overs and update vpoller-client docstrings
Check the client message for proper message attribute type as well
Add a new 'vm.discover' method for discovery of Virtual Machines on a vSphere host
Implement a 'vm.poll' method for retrieving properties of VirtualMachine objects
Implement a 'datacenter.discover' method for discovering of Datacenter objects
Add redumentary 'datacenter.poll' method
Implement 'cluster.discover' method for discovering ClusterComputeResource objects
Add 'cluster.poll' method for retrieving ClusterComputeResource object properties
Add 'todo' entries for some of the methods so that we don't forget about implementing them :)
Use '<method>.get' for the poll methods as it makes more sense to 'get' a property
Use a more consistent message for all objects we want to discover and poll
s/command/method as this is the convention we use
Documentation update