String interpolation should be delayed to be handled by the logging code, rather than being done at the point of the logging call. See the oslo i18n guideline * https://docs.openstack.org/oslo.i18n/latest/user/guidelines.html#adding-variables-to-log-messages and * https://github.com/openstack-dev/hacking/blob/master/hacking/checks/other.py#L39 Closes-Bug: #1596829 Change-Id: Ibba5791669c137be1483805db657beb907030227