Fixed wrong array type in dummy CS

[JeanLucPons]

This PR solve a bug in the dummy CS triggered by the BPMArray.

>           return self.__aggregator.get().reshape(len(self.__bpms),2)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E           AttributeError: 'list' object has no attribute 'reshape'

pyaml/arrays/bpm_array.py:20: AttributeError