Fixed missed translatable string inside exception
Fixed missed translatable string inside exception

A string inside an exception was not being passed to
i18n translation so it will only show up as English if it
was ever thrown.

Here is a grep I used to make sure there were no more
exception strings that were not being passed to translations
before they were thown.
grep -r 'exception' . | grep '("' | grep -v '_'

Change-Id: I51a0d6d5b1d4053c380c8be5a0e6ac4e61985b81

ajayaa/keystone,klmitch/keystone,mahak/keystone,mahak/keystone,dims/keystone,rajalokan/keystone,cernops/keystone,openstack/keystone,rajalokan/keystone,rajalokan/keystone,himanshu-setia/keystone,dims/keystone,openstack/keystone,maestro-hybrid-cloud/keystone,ilay09/keystone,himanshu-setia/keystone,openstack/keystone,klmitch/keystone,maestro-hybrid-cloud/keystone,mahak/keystone,ajayaa/keystone,ilay09/keystone,ilay09/keystone,cernops/keystone