Change: Ib56ee8bfd182c031e468c503acb0cd75daea8c40 broke vmware-nsx
L2 gateway plugin for master and mitaka release. Due to this the
l2 gateway plugin for vmware-nsx would not load.
This patch makes the required changes in vmware-nsx to load l2gw
plugin.
This patch also adds a README file to include steps to bring up
L2 gateway plugin with devstack.
Closes-Bug: #1573327
Change-Id: I433c7f51df80ff6ea4250e38c981ffb363cf1b17
f70a8c4b8c