reproducible opensuse: try decoding the input before giving it to json

Traceback (most recent call last):
  File "./reproducible_opensuse_import_json.py", line 22, in <module>
    ostatus = json.loads(ofile)
  File "/usr/lib/python3.5/json/__init__.py", line 312, in loads
    s.__class__.__name__))
TypeError: the JSON object must be str, not 'bytes'

Signed-off-by: Mattia Rizzolo <mattia@debian.org>