Extract CommonDBMixin to a separate file

db_base_plugin_v2 imports too much modules that are not necessary
usually, so extract CommonDBMixin in different file.
Plus using db_base_plugin_v2 for some types of modules can lead to
cycles in imports, this refactoring should resolve the issue.

Closes-Bug: #1340145
Change-Id: Idb027d7c5cee2d5bc7598f805c56c55fd4aca048
Add L3 Extension for Distributed Routers

This patch introduces the model and extension
framework for implementing distributed virtual
routing on top of Open vSwitch.

A new admin-only 'distributed' (as opposed to a
'centralized' or legacy-mode) attribute is added
to the API router resource. It is possible to convert
an existing (centralized) router to a distributed
one; the opposite conversion, even though allowed by
the API, may not be honored by the underlying
plugin implementation and an appropriate error will
be reported.

When creating a router (regardless of the user role),
Neutron will rely on a system wide configuration, whose
default currently allows to create 'centralized' routers.

Tests are added for basic unit coverage; when the first
building blocks for neutron-testing-refactor
are complete, functional testing will be added.
This is because we should be moving away from how
extension tests have been done up until now.

Partially-implements: blueprint neutron-ovs-dvr

DocImpact

Change-Id: I7227fbe2718eba6665a5afb5dcaaaa77b341091f
Authored-by:    Swaminathan Vasudevan <swaminathan.vasudevan@hp.com>
Co-Authored-By: Armando Migliaccio <armamig@gmail.com>
L2 Model additions to support DVR

This patch introduces the models, the DB migrations
and the config options required by the L2 layer to
support DVR east/west traffic.

These changes will be used by the control-plane made
of ML2, L2pop and L2 agent.

Two new configuration options have been introduced:
'dvr_base_mac' is used to set DVR MAC addresses apart
from tenant ones (every distributed router will have
ports being created on compute hosts) and
'enable_distributed_routing' is used to enable dvr
support in the L2 agent. This gives the capability of
rolling out the dvr functionality in stages.

Partially-implements: blueprint neutron-ovs-dvr

DocImpact

Change-Id: Iab6505f239d2c4c9bcbf4e32a292d7b4b5320c8e
Authored-by: Vivekanandan Narasimhan <vivekanandan.narasimhan@hp.com>
Co-Authored-By: Armando Migliaccio <armamig@gmail.com>
RPC additions to support DVR

This patch introduces the RPC contract changes
required for both the server (plugin) and agent
to propagate and retrieve additional information
about Distributed Routers, like MAC addresses
and Port Bindings.

Partially-implements: blueprint neutron-ovs-dvr

Change-Id: I04a2ee5fceea79d2786c799178f8dd1675925a39
Authored-by: Vivekanandan Narasimhan <vivekanandan.narasimhan@hp.com>
Co-Authored-By: Armando Migliaccio <armamig@gmail.com>
ML2 additions to support DVR

This patch introduces the changes necessary to
support DVR at Layer 2 with ML2, and L2pop.

Partially-implements: blueprint neutron-ovs-dvr

Change-Id: I709d877e7df83728868e68e023e6a37bb2e11704
L2 Agent-side additions to support DVR

This patch introduces changes to the L2 agent, whereby the L2 agent
relies on a DVR component that takes care of the port wiring and the
management of tunnels in face of topology changes due to the life
cycles or VM's as well as the life cycles of distributed virtual
routers.

Support for DVR needs to be explicitly enabled. Default behavior
remains unchanged.

Partially-implements: blueprint neutron-ovs-dvr

Change-Id: If75225898a6f0aeea8b0300b711ca7e01f6b4f9a
Add L3 Scheduler Changes for Distributed Routers

This patch implements the L3 Scheduler changes for the
Distributed Virtual Routers.

Partially-implements: blueprint neutron-ovs-dvr

Change-Id: I407c3d639ebdf885b1418bceac7cfc251e7eba1f
Co-Authored-By: Carl Baldwin <carl.baldwin@hp.com>
Co-Authored-By: Armando Migliaccio <armamig@gmail.com>
Modify L3 Agent for Distributed Routers

This patch is an enhancement to the existing L3 Agent.
This allows the L3 Agent to support distributed routers
by enhancing the router object to function across
multiple nodes.

Utilized two new types of namespaces:

- FIP to handle multiple VM fips and routers per node
- SNAT to handle centralized SNAT per router

Rules and tables are enhanced and added to support routing
across distributed routers without going to a centralized
router.

Finally, a new configuration param 'agent_mode' is introduced
and it controls what the L3 agent can do: the available values
are: 'legacy', 'dvr', 'dvr_snat' (more details inline).

The l3-scheduler uses the newly introduced agent_mode to
determine what L3 agent to select during the scheduling
process.

Partially-Implements: blueprint neutron-ovs-dvr

DocImpact

Change-Id: Icead821bb74372b15aac2e5cefe8ad7f08c037ab
Co-Authored-By: Rajeev Grover <rajeev.grover@hp.com>
Merge DVR patches together