python: Open file in binary mode

python: Open file in binary mode

The XML parser wants byte strings, not unicode strings.

In both Python 2 and 3, opening a file without specifying the mode will
open it for reading in text mode ('r').

On Python 2, the read() method of the file object will return byte
strings, while on Python 3 it will return unicode strings.

Explicitly specifying the binary mode ('rb') makes the behaviour
identical in both Python 2 and 3, returning what the XML parser
expects.

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