python3: python3 binary/text data compatbility

Python3 enforces the distinction between byte strings
far more rigorously than Python 2 does; binary data
cannot be automatically coerced to or from text data.

Use six to provide a fake file object for textual data.
It provides an alias for StringIO.StringIO in python2
and io.StringIO in python3

Change-Id: I65897bb0cca2cbeb5819a769b98645c9eb066401
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "python3: python3 binary/text data compatbility"