Require neutronclient>=2.3.4

New client includes fix that is required for neutron builds that include the
following commit: 15a912b1ca3c24ba8851b8b77d6de8027e120d78

Change-Id: If0eab1b5dd102cc5ceb7720a8465ee47a708839d
Partial-Bug: #1280941
Merge "Require neutronclient>=2.3.4" into stable/havana