Add a hacking rule for string interpolation at logging

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

tox.ini

@@ -55,7 +55,7 @@ filename = *.py,app.wsgi
 show-source=True
 ignore= H105,E123,E226,N320,H202
 builtins= _
-enable-extensions = H106,H203
+enable-extensions = H106,H203,H904
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build,*sqlalchemy/alembic/versions/*,demo/,releasenotes
 
 [testenv:wheel]