Stop using openstack.common.exception

The openstack.common.exception has been deprecated and removed from
oslo-incubator. Therefore, Ceilometer should follow the recommendation
and stop the usage of this file altogether.

Closes-Bug: #1208734
Change-Id: Ida4530d2f966f97b980db333f08a990250b7b68d
Merge "Stop using openstack.common.exception"