shim l3 exceptions with neutron-lib
shim l3 exceptions with neutron-lib

Commit I81748aa0e48b1275df3e1ea41b1d36a117d0097d added the l3 extension
API definition to neutron-lib and commit
I2324a3a02789c798248cab41c278a2d9981d24be rehomed the l3 exceptions.
While we'd like to just consume the changes in neutron, many consumers
use the l3 extension [1] and have branching code that depends on
checking the l3 exceptions. Therefore we can't switch consumers over
using a one-step approach as they will be branching off lib exceptions
while neutron is raising it's own exceptions.

This patch shims the neutron l3 exceptions to ref neutron-lib's. This
will allow us to move consumers over to the l3 code in lib and then
finally consume the l3 changes in lib (removing the shims as well).

[1] http://codesearch.openstack.org/?q=from%20neutron.extensions%20import%20l3

Change-Id: Ifd79eb1a92853e49bd4ef028e7a7bd89811c6957

mahak/neutron,huntxu/neutron,noironetworks/neutron,eayunstack/neutron,noironetworks/neutron,openstack/neutron,eayunstack/neutron,openstack/neutron,mahak/neutron,mahak/neutron,huntxu/neutron,openstack/neutron