python: Specify the template output encoding

python: Specify the template output encoding

We're trying to write a unicode string (i.e decoded) to a file opened
in binary (i.e encoded) mode.

In Python 2 this works, because of the automatic conversion between
byte and unicode strings.

In Python 3 this fails though, as no automatic conversion is attempted.

This change makes the scripts compatible with both versions of Python.

Signed-off-by: Mathieu Bridon <bochecha@daitauha.fr>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>