image-fuzzer: Open image files in binary mode

This probably never caused problems because on Linux there's no
actual newline conversion happening, but on Python 3 the
binary/text distinction is stronger and we must explicitly open
the image file in binary mode.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20191016192430.25098-2-ehabkost@redhat.com
Message-Id: <20191016192430.25098-2-ehabkost@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

tests/image-fuzzer/qcow2/layout.py

@@ -503,7 +503,7 @@ def coin():
 
     def write(self, filename):
         """Write an entire image to the file."""
-        image_file = open(filename, 'w')
+        image_file = open(filename, 'wb')
         for field in self:
             image_file.seek(field.offset)
             image_file.write(struct.pack(field.fmt, field.value))