Add linuxbridge mechanism support for ML2 plugin

Add support for the Linux Bridge mechanism. It includes support
for VXLAN tunneling and L2 population.

Conflicts:
  manifests/plugins/ml2.pp

Change-Id: I0faca3d4603c6eacbbaa61adef7b742b3a262641
(cherry picked from commit bddd060a28b0f303eaee3e5383fa1e34a9eb2aea)
Support for Cisco ML2 Mech Driver

Partially Implements: blueprint support-ml2-nexus-driver

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