Implements sync mechanism between Neutron and Nuage VSD

This will sync resources between Neutron and VSD based on
the configuration parameters. "enable_sync" will enable/disable
the sync and "sync_interval" will control the time interval
between consecutive sync cycles.

DocImpact

Change-Id: I6730bf0166dfd1e35795b679293a2831b5afbc75
Implements: blueprint nuage-neutron-sync
BSN: Bind external ports in ML2 driver

Add a binding capability to the Big Switch ML2 mechanism
driver to mark external ports as bound. Ports with the
owner type 'neutron:external_port' will be assigned to the first
VLAN segment available in the network. The port update operation
will then carry the HOST ID with the identifier to the backend
for the necessary fabric configuration.

Implements: blueprint bsn-ml2-ext-attach
Change-Id: I7b749ba5ef9a47b45be24f77656a10ed38e5e6ae
Merge "Implements sync mechanism between Neutron and Nuage VSD"
Merge "BSN: Bind external ports in ML2 driver"