Ml2 Mechanism Driver for OVSvApp Solution

Ml2 Mechanism Driver for OVSvApp Solution

With the introduction of stackforge/networking-vsphere project
which includes the OVSvApp L2 agent for doing vsphere networking
using neutron.

We need to have thin mechanism driver in neutron which integrates
the ml2 plugin with the OVSvApp L2 Agent.

The mechanism driver implements the abstract method given in
mech_agent.SimpleAgentMechanismDriverBase.

Closes-Bug: 1426365
Partially-implements: blueprint core-vendor-decomposition

Change-Id: I57b2abb58671b8a1c6a2734959346ddeb8fda988