python3 compatibility fix for mdc channels
In python2:
>>> str(mdc_channels.values()).replace("'",'')
'[seriesH1, seriesL1]'
In python3
'dict_values([seriesH1, seriesL1])'
Change to:
>>> str(list(mdc_channels.values())).replace("'",'')
'[seriesH1, seriesL1]'
which behaves identically in python2 and python3.