LOG.exception for mech dict extend failure
LOG.exception for mech dict extend failure

We generate a new exception here instead of re-raising
so we need to use LOG.exception to make debugging easier.

TrivialFix

Change-Id: Iccb2c8576729062ab0d881c867d1e44811ecf931

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