'Get the total number of volumes associated with a masking view.
:param serial_number: the array serial number
:param maskingview_name: the name of the masking view
:returns: num_vols, parent_sg_name'

def _get_num_vols_from_mv(self, serial_number, maskingview_name):

    parent_sg_name = self.rest.get_element_from_masking_view(serial_number, maskingview_name, storagegroup=True)
    num_vols = self.rest.get_num_vols_in_sg(serial_number, parent_sg_name)
    return (num_vols, parent_sg_name)
