regression/clear_datastore no longer works

[dhermes]

As of b343acf running

$ python regression/clear_datastore.py

fails because the backend returns

Exception: Request failed. Error was: queries inside transactions must have ancestors

To see an example query, insert the following:

>>> print query._pb
projection {
  property {
    name: "__key__"
  }
}
kind {
  name: "Character"
}
limit: 20

I'm fairly certain the backend has changed, but I'm not 100% sure.

Either way, this isn't super pressing right now since there are lot's of ways to delete entities that were accidentally created.