Fix importing old path for exceptions

The network_ip_availability plugin uses old path for exceptions.
This patch fixes the path and adds negative test for the exception.

Change-Id: I9021f76e21b386f371ff73b926553611ab87fb66
Closes-bug: #1657137
2 files changed
tree: fb3ebaa7121297edc6aa1d8c5d9bff47a71ef062
  1. neutron/