UnicodeEncodeError when run under Python 2.7

checkbox-support needs to work well under Python 2.7 since it's used in hexr which runs under 2.7.

James reported this:

Traceback (most recent call last):
  File "apps/uploads/checkbox_parser.py", line 228, in <module>
    sys.exit(main())
  File "apps/uploads/checkbox_parser.py", line 219, in main
    messages = parse_stream(stream)
  File "apps/uploads/checkbox_parser.py", line 22, in parse_stream
    parser.run(TestRun, messages=messages)
  File "/home/jjesudason/Documents/PES/hexr/hexr/local/lib/python2.7/site-packages/checkbox_support/parsers/submission.py",
line 1152, in run
    self.parseRoot(result, root)
  File "/home/jjesudason/Documents/PES/hexr/hexr/local/lib/python2.7/site-packages/checkbox_support/parsers/submission.py",
line 1125, in parseRoot
    parser(result, child)
  File "/home/jjesudason/Documents/PES/hexr/hexr/local/lib/python2.7/site-packages/checkbox_support/parsers/submission.py",
line 936, in parseContext
    result.addContext(text, command)
  File "/home/jjesudason/Documents/PES/hexr/hexr/local/lib/python2.7/site-packages/checkbox_support/parsers/submission.py",
line 643, in addContext
    text = text.decode("utf-8")
  File "/home/jjesudason/Documents/PES/hexr/hexr/lib/python2.7/encodings/utf_8.py",
line 16, in decode
    return codecs.utf_8_decode(input, errors, True)
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in
position 99516: ordinal not in range(128)
No JSON object could be decoded

How to reproduce:
- Run the attached submission.xml through the hexr checkbox_parser script using Python 2.7. Assuming up-to-date checkouts of lp:hexr and lp:checkbox, run this inside the hexr tree:

PYTHONPATH=/path/to/checkbox/checkbox-support python apps/uploads/checkbox_parser.py sample-with-modaliases-dkms.xml >/dev/null

Expected result:
- Nothing, since we're sending the good output to /dev/null

Actual result:
- Trace as seen above.

And as noted, running the same thing with python3 doesn't return anything (meaning it was parsed correctly).