Cisco APIC ML2 mechanism driver, part 1

This set of changes introduces a mechanism driver for the
Cisco APIC. Please see the blueprint for more information.

The review is submitted in two parts:
- Part 1 (this one)
    o APIC REST Client
    o APIC data model and migration script
    o APIC configurations
- Part 2 (dependent on part 1)
    o APIC mechanism driver
    o APIC manager

Partially implements: blueprint ml2-cisco-apic-mechanism-driver

Change-Id: I698b25ca975fed746107ee64f03563ef1a56e0ef
Merge "Cisco APIC ML2 mechanism driver, part 1"