How to handle done signal in PVPositioners

[gfabbris]

In the past we done something like:

def move(self, *args, **kwargs):
    self.done.put(0)
    return super().move(*args, **kwargs)

The above doesn't work well for some cases, like the undulatory. So it looks like the best would be:

def move(self, *args, **kwargs):
    status = super().move(*args, **kwargs)
    self.done.get()
    return status

but this needs to be tested.

[gfabbris]

This may be best implemented like discussed in #101.