Get complete task history

Hi,

is there a method to access the **complete** task history? I've only seen the _recentTask_-Property on [TaskManager](https://github.com/vmware/pyvmomi/blob/master/docs/vim/TaskManager.rst) and [ManagedEntity](https://github.com/vmware/pyvmomi/blob/master/docs/vim/ManagedEntity.rst) which doesn't cover completed tasks that are older than 10 minutes.

All the best,
retooth
