Refactor the vPoller Proxy module
Better way to define the management methods we support
Add 'shutdown' and 'status' methods for vPoller Proxy
Add a missing comma
Use a reference to the object method, and do not call the method
The vSphereAgents always return result in JSON

* Also remove for now the Zabbix parts until we have a better way
   to add support for Zabbix, perhaps as a separate module
A new command-line switch -m <method> available for specifying the method we want

* No more -c <cmd>, -D and -H switches