python3: Fix traceback while running python3.

Python3 enforces the distinction between byte
strings and text strings more rigorously than
python2. So use six.text_type where approiate
and six.string_types.

Change-Id: Iaab049fff97278d94fd7ab932a514949094a949a
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "python3: Fix traceback while running python3."