intg: Fix python3 issues
NamedTemporaryFile use the default mode 'w+b'
and we tried to write strings. It is not a problem on python2
but failed on pyhton3
Python module ctypes directly uses C functions from libraries.
C functions usually expect/returns "char *" when string is expected.
But python3 uses unicode for string. Decoding returned bytes
("char *") to unicode strings simplify tests in python3.
Otherwise we would need to convert bytes to string in each assertion.
Reviewed-by: Martin Basti <mbasti@redhat.com>
(cherry picked from commit bac4458c89a589055ae3daf4f72cc7dba886264a)