Support for Cisco ML2 Mech Driver

Partially Implements: blueprint support-ml2-nexus-driver

Change-Id: I5e0486c9db22abfcbab205e6f57bbafe8f0b5dd4
(Cherry-picked from master:
68ddc7a81145999594a4b52d2e59e5874aac0d10
3848a2b411f9a78b7f773b789a2d57daff176cc5)
Merge "Support for Cisco ML2 Mech Driver" into stable/icehouse