Introduces a new property "enable_neutron_dvr", along with the
appropriate service and template changes to allow DVR.
Closes-Bug: #1623463
DocImpact: dvr changes network data paths and adds requirements for NICs
Co-Authored-By: Vladislav Belogrudov <vladislav.belogrudov@oracle.com>
Change-Id: I87a26e9258228ae2ccb76be1e5f0bb44fac128df