Make the Kernel event handler tests work again

Make the Kernel event handler tests work again

- Strip the underscores in CtfTmfEventField's. We need to save a
  value here (we can't use the parser's lookupDefinition()), so
  might as well save it with no underscore.
- Use the getSource() as a way to get the event name. This is still
  waiting on the final trace model. We are bypassing the EventTypeManager
  for now
- Use getTimestampValue() to check for a nullEvent, getTimestamp
  always return the ITmfTimestamp object now, so it's not null!