Stop using WritableLogger() which is deprecated
Stop using WritableLogger() which is deprecated

With Eventlet 0.17.2, we can directly pass the logger instance. This
allows us to deprecate/remove the WritableLogger class from oslo.log.

Change-Id: Ic42332467c965b301af96e85b130120a283ba799
Closes-Bug: #1524860

openstack/designate,openstack/designate,openstack/designate,grahamhayes/designate,grahamhayes/designate,grahamhayes/designate