Use openstack.common.exception
Use openstack.common.exception

Fixes bug #1013040

1. Edit openstack-common.conf and import openstack.common.exception
2. Remove redundant code

Change-Id: Ia440422e283f8e6796d9a1f720d73b3bcf2f981e

openstack/networking-mlnx,stackforge/networking-mlnx,moshele/networking-mlnx,stackforge/networking-mlnx,openstack/networking-mlnx,moshele/networking-mlnx-master