Add a TODO entry to create a task registry interface
New tasks can be added only if they are callable()
The vSphere task we add is also an attribute of the VSphereAgent class
Add a TODO entry for implementing a BaseAgent class
Style fix
Exceptions raised by tasks should not be propagated to the Workers

* An Agent task could fail any time, but such exceptions should not be
  propagated to the Workers.
* A failing task should not bring a Worker to it's knees
Add a todo entry to implement a TaskResult class