python3: Fix imports for py2/py3

Python3 reorganized the standard library and moved several functions
to different modules. Six provides a consistent interface
to them through the fake six.moves module.

However, the urlparse, urllib2, etc modules have been combined
into one module which Six does not support so we do it via
py3kcompat.

Modules such as StringIO and CStringIO have been removed
completely so we use the io module.

Change-Id: I53adac11b634de2c710fc39def36bcec96366710
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "python3: Fix imports for py2/py3"