Updated openstack/openstack
Project: openstack/keystone  2f14f3a95fcf9d86faf775d72234507681cfd0fa

Mock doesn't have assert_called_once()

Mock doesn't provide assert_called_once, switch to the right
function.

Change-Id: I0e97f2e3b5a0e0b36c2ae276bdc67b00e9f2179f