python: Adapt to virevent rename

python: Adapt to virevent rename

With our recent renames under src/util/* we forgot to adapt
python wrapper code generator. This results in some methods being
not exposed:

$ python examples/domain-events/events-python/event-test.py
Using uri:qemu:///system
Traceback (most recent call last):
  File "examples/domain-events/events-python/event-test.py", line 585, in <module>
    main()
  File "examples/domain-events/events-python/event-test.py", line 543, in main
    virEventLoopPureStart()
  File "examples/domain-events/events-python/event-test.py", line 416, in virEventLoopPureStart
    virEventLoopPureRegister()
  File "examples/domain-events/events-python/event-test.py", line 397, in virEventLoopPureRegister
    libvirt.virEventRegisterImpl(virEventAddHandleImpl,
AttributeError: 'module' object has no attribute 'virEventRegisterImpl'