Change obj.next() calls to next(obj).

This is necessary for Python 3 compatibility.

Done using:

  $ py=$( (g grep -l -E '^#!.*python';find -name '*.py' -printf '%P\n';) | \
    sort -u | grep -v README.sh4)
  $ futurize -w -f libfuturize.fixes.fix_next_call $py

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20180608122952.2009-4-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>