python3: Fix unicode and gettext

In Python 2, ensure that the _() that gets installed into built-ins
always returns unicodes.  This matches the default behavior under Python
3, although that keyword argument is not present in the Python 3 API.

Change-Id: If9e7bb07f389149b3dcf4314f6b2b4faf2b659d0
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "python3: Fix unicode and gettext"