heat: allow overriding Heat/Neutron private IP for DPDK tests

heat: allow overriding Heat/Neutron private IP for DPDK tests

For some L2/L3 DPDK testcases we need to use a custom
IP address space different from what Heat provides.

These testcases require port_security_enabled = False so
Neutron should allow for unrestricted L2 traffic.

This will work because we bind the ports to DPDK and thus
don't need DHCP.

  vnf_0:
    floating_ip: true
    placement: "pgrp1"
    network_ports:
      mgmt:
        - mgmt
      uplink_0:
        - xe0:
            local_ip: 10.44.0.20
            netmask: 255.255.255.0
      downlink_0:
        - xe1:
            local_ip: 10.44.0.30
            netmask: 255.255.255.0

Also fixup flake8 errors in unittests

Change-Id: Id29dfffa692f16fb1f526d208db43e476e2f7830
Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>