Big Switch Networks code split

Big Switch Networks code split

This commit removes all of the Big Switch Networks
code from the tree and replaces it with the import
statements required to pull in the entry points
from the new 'bsnstacklib' module.

All patches for BSN code should now be submitted
to the stackforge/networking-bigswitch project.

Partial-implements: blueprint core-vendor-decomposition
Change-Id: I4d83c9fd6a2953c329c247c78425f8e3280e8a42