Remove usage of WritableLogger from oslo_log
Remove usage of WritableLogger from oslo_log

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

So there is no need to maintain class `WritableLogger` in our code.

Change-Id: Ibeedb65ebfb0cd8bc0ffe24069b390931d8dfe4b
Closes-Bug: #1440773

noironetworks/heat,steveb/heat,jasondunsmore/heat,openstack/heat,steveb/heat,noironetworks/heat,jasondunsmore/heat,openstack/heat,cwolferh/heat-scratch,cwolferh/heat-scratch