Fix default encoding issue with python 2.6

This change addresses issue #38: "fix unicode handling issues".

The issue was originally reported against neutron client
(https://bugs.launchpad.net/python-neutronclient/+bug/1189112) but
was tracked down to the fact that python 2.6 does not set the default
encoding for sys.stdout properly. A change to python 2.7 fixes the
problem there and later (http://hg.python.org/cpython/rev/e60ef17561dc/),
but since cliff supports python 2.6 it needs to handle the case
explicitly.

Change-Id: Id06507d78c7c82b25f39366ea4a6dfa4ef3a3a97