Use the same logic for returning the samples from the various MPI tasks
as for working with them in each task.

Gordian Edenhofer authored Mar 25, 2020 and Martin Reinecke committed Mar 25, 2020

Fix a bug which was introduced in eded7903 making it impossible to
access the sample property of a KL with mirrored samples as a list can
not be added to a tuple in python.

This behaviour is not intended according to the docstring.