This patch add a script to create v2plugin rootfs.
1. use local unix socket for v2plugin
2. add config.json for v2plugin
3. Add scripts to build v2plugin rootfs
4. Update devstack to use v2plugin
Change-Id: I91d352a963840f33d1d2f9cea17ab6ac777d22bc
Related-Bug: #1668486
Partially-Implements: BP docker-v2plugin