ML2 mechanism driver for SR-IOV capable NIC based switching, Part 2

This set of changes introduces SRIOV NIC Agent to run with
ML2 mechanism driver for SR-IOV capable NIC based switching.
This is the second part of a 2 part commit.

The review is submitted in two parts:
- Part 1
    The Mechanism Driver to support port binding for SR-IOV virtual
	functions of SRIOV capable switching NICs.

- Part2 (this part)
    The SRIOV NIC Based L2 Agent.
	Use  configurable list of mappings physical_networks to PF
        interfaces and configurable list of mappings PF interfaces
        to list of excluded VFs to get list of Virtual Functions that agent should manage.
	Current implementation supports admin state updates.

Co-authored-by: Samer Deeb <samerd@mellanox.com>
Partially implements: blueprint ml2-sriov-nic-switch

Change-Id: I533ccee067935326d5837f90ba321a962e8dc2a6
Merge "ML2 mechanism driver for SR-IOV capable NIC based switching, Part 2"