Added LBaaS and FWaaS documentation for the NVP plugin

Added documentation to describe the LBaaS and FWaaS services when used
with the NVP plugin. The documentation points out the differences from
the community reference implementation and shows how to configure the
services with the NVP plugin.

Change-Id: I89a70b28d598e8405ebe6af0297a3d7be3255eeb
backport: none
Closes-Bug: #1247281
Merge "Added LBaaS and FWaaS documentation for the NVP plugin"