Remove unused exceptions
Remove unused exceptions

Some of the exceptions defined in exception.py module are not used
anywhere. Some of them were added at the initial import from neutron
in the commit: 8aff29509f1f6cfc73973b8da3e55ed559ae1112

This patch removes all such unused exceptions.

TrivialFix
Change-Id: I630960a5023e6ed776939d7c7d36a3d7d4b489e8

openstack/tacker,stackforge/tacker,openstack/tacker,stackforge/tacker,openstack/tacker