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.

merged

mentioned in commit 352ae02d