NEC plugin: Fix nec-agent unexpected exit due to RPC exception

Changes nec-agent to catch RPC exceptions in the main
daemon loop. It fixes the following two bugs.

- nec-agent dies with RPC timeout in secgroup RPC
  (Closes-Bug: #1235106)

- port_added message can be dropped when RPC timeout occurs
  (Closes-Bug: #1235111). Moves exception catch from PluginApi
  to the main daemon loop.

test_nec_agent.py is added during Havana.
The base class and related tests are imported.

Change-Id: I12394b739fc35bff271543f4625c5e3152e534ae
(cherry picked from commit 3df505e448d38929c20721b22d81e47bf917af6a)
Make Quantum NVP plugin future-versions friendly

This patch enables the plugin to deal correctly with
newer versions of the NVP platform; this is done by
allowing the plugin to fall back to the closest known
version of the NVP platform. This is acceptable behavior
as L2/L3 operations implemented by the platform are most
certainly backward compatible.

This patch also improves test coverage for this part of the
code, which is critical to the correct behavior of the plugin.

Fixes bug #1217479

Conflicts:

	neutron/tests/unit/nicira/test_nvplib.py
	quantum/plugins/nicira/nicira_nvp_plugin/nvplib.py

Change-Id: Idddad8b0a5a1709683611bac6f239b18f90ee99b
Merge "NEC plugin: Fix nec-agent unexpected exit due to RPC exception" into stable/grizzly
tmp

grep -nR zyluo.\\+dhcp_init * | awk '{print $5 $0}' | sort

Change-Id: Iedf1f5804e07639259c7689ea33fb305f0fa2a52