container-image-prepare: disable logging on the task
container-image-prepare: disable logging on the task

We already log the output of the tripleo-container-image-prepare
command in ContainerImagePrepareLogFile, there is no need to
also have the output in the ansible.log, it's just too much.

Change-Id: I3d20cd70bd14dc00078d68cd3f9a06353a7ac471

openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates,dprince/tripleo-heat-templates