NSX: properly handle floating ip status

Ensure the floating IP status is put ACTIVE or DOWN when it
is associated or disassociated.
This is done directly on the plugin class as the NSX backend
applies relevant NAT rules synchronously.

Change-Id: Ie747c4eae2ac33016fdabaade2335f7d2d24eec9
Closes-Bug: #1334708
Avoid notifying while inside transaction opened in delete_port()

delete_port() calls to disassociate_floatingips() while in transaction.
The latter method sends RPC notification which may result in eventlet
yield. If yield switches a thread to another one that tries to access
the same floating IP object in db as disassociate_floatingips() method
does, we're locked and get db timeout.

We should avoid calling to notifier while under transaction.

To achieve this, I introduce a do_notify argument that controls whether
notification is done by disassociate_floatingips() itself or delegated
to caller. Callers that call to disassociate_floatingips() from under
transactions should handle notifications on their own. For this,
disassociate_floatingips() returns a set of routers that require
notification.

Updated drivers to reflect new behaviour. Added unit test.

Change-Id: I2411f2aa778ea088be416d062c4816c16f49d2bf
Closes-Bug: 1330955
Implementation of LBaaS Version 2

Added alembic migrations that add new tables for the new object model.
Added new loadbalancingv2 extension.
Added new LoadBalancerPluginv2 class to plugin.py module and unit tests.
Added new loadbalancer_dbv2.py module and unit tests.
Added shim layer to translate new plugin to old style driver and vice versa.

Change-Id: I43270fdf9cd52a57274575ecea502f660ff0d5a9
Co-authored-by: Brandon Logan <brandon.logan@rackspace.com>
Co-authored-by: Vijayendra Bhamidipati <vbhamidipati@paypal.com>
Co-authored-by: Craig Tracey <Craig.Tracey@gmail.com>
Co-authored-by: Phillip Toohill <phillip.toohill@rackspace.com>
Co-authored-by: Dustin Lundquist <dustin@null-ptr.net>
Implements: blueprint lbaas-api-and-objmodel-improvement
python 2.6 fixes
fix pep8
Merge branch 'bp/lbaas-api-and-objmodel-improvement' of https://github.com/oslbaas/neutron into bp/lbaas-api-and-objmodel-improvement