Some fixes for zbar-python build
In order to be able to build a zbar-python, we need to address
some small things. Among them, there's a requirement to use
"python3" at python's test script.
IMHO, that's a bad idea, at least upstream, as the same script also
works with python2 when using pygtk (also supported by ZBar).
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>