next() is incompatible in test_network_ip_availability.py

Replace iter.next() with next(iter)

Change-Id: I43dfda97451d2893a5fca480b79f14da479c01df
Closes-Bug: #1598527
1 file changed
tree: 916d4f1f20a28e13eb3d10a9b0683f36b458d3ea
  1. neutron/