NSX plugin: return 400 for invalid gw certificate

Gateway certificates are validated by the NSX backend.
The code currently treats a failure in certification
validation as a backend failure and therefore returns
a 500 status code.

This patch changes this behaviour by returning a 400
status code and an appropriate error description.
To this aim a handler for 400 errors has been added to
the NSX API client.

Closes-Bug: #1293508

Change-Id: I196f14337e47cd40710a6d8a30bbe1cac5ffe05b
Update BigSwitch Name to its correct name

Update Neutron documentation and code comments to replace
"BigSwitch" name to "Big Switch"

Closes-Bug: #1299145
Change-Id: I7c14f6170871b361c8929898ee6af5d1a1f41714
Removing vim header lines

Simply removes the vim header line and the empty line
following it (when present) for files in the api, db, and
extenssions base directories. In one single _init_ file in
this patchset, all comment lines are removed.

Change-Id: I81b7168dc2ad74b8c30a87e50a531e157851499e
Partial-Bug: 1229324
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 "NSX plugin: return 400 for invalid gw certificate"
Merge "Removing vim header lines"
Merge "Stop using portbindings_db in BSN ML2 driver"
Merge "Return 409 for second firewall creation"
Merge "Update BigSwitch Name to its correct name"