Make pyflakes-0.8 happier

Without this patch, pyflakes-0.8.1 complains about

 ./vdsm/network/sourceroute.py:153: list comprehension redefines 'rule' from line 146

I do not agree with this complaint of newer pyflakes versions, but I do
not mind enough to fight it.

Change-Id: I507cb00a47279a6b119f280a1ac787c2071f681f
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28468
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>