Add a VIF driver for IOVisor engine

Implements blueprint iovisor-vif-driver

Unit Test is included
Follows the same structure that OVS and Qbh drivers
Includes the rootwrap config to allow calls to ifc-ctl for managing IOVisor engine.

Change-Id: I346b4d84a6e48d56f307349ed681355d26710ecd
Move resource usage sync functions to db backend

Resource usage sync functions was declared in nova/quota.py, and
using db.api public methods. This functions was moved to database
backend implementation, so now sync functions can use private
methods of database backend, and session attribute can be removed
from this public methods, and even some public methods can be removed.

Blueprint: db-session-cleanup

Change-Id: I63eeb18b8ede4b4263ee553d4e70633de463e0c4
Merge "Add a VIF driver for IOVisor engine"
Merge "Move resource usage sync functions to db backend"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp