Stop using portbindings_db in BSN ML2 driver

Avoids using the portbindings_db in the Big Switch
ML2 driver since ML2 has deprecated that database for
its own version that tracks the same information.

Also eliminates unnecessary 'binding_host' field since
it is now always the same as as the 'portbinding:host_id'
field.

Closes-Bug: #1300628
Change-Id: I17d47cb446cdd2e989c3e0d01b797a81309faaa7
Return 409 for second firewall creation

Second firewall creation returns 500, but it is an expected behavior
of firewall reference implementation and an internal server error
should not be returned.

Change-Id: I9f537b238007d35172e2504591d9d3568ba3a41a
Closes-Bug: #1301105
Merge "Stop using portbindings_db in BSN ML2 driver"
Merge "Return 409 for second firewall creation"