Decode received data in byte type to str type

json.loads in Python 3.5 doesn't accept a byte-type values so we need to
decode it. Note that this is specific to Python 3.5; Python 2.7 and 3.6
accept byte-type values.

Change-Id: I490f8e0f02a6ce277f86e75b32d1210bfcca8d49
Signed-off-by: Carlos Goncalves <carlos.goncalves@neclab.eu>