Iterate over all registered plugins or plugin points and prepare to add
        them to database.

def available(self, src, dst, model):
        """
        Iterate over all registered plugins or plugin points and prepare to add
        them to database.
        """
        for name, point in six.iteritems(src):
            inst = dst.pop(name, None)
            if inst is None:
                self.print_(1, "Registering %s for %s" % (model.__name__,
                                                          name))
                inst = model(pythonpath=name)
            if inst.status == REMOVED:
                self.print_(1, "Updating %s for %s" % (model.__name__, name))
                # re-enable a previously removed plugin point and its plugins
                inst.status = ENABLED
            yield point, inst