Use auto-model-class for ContainerImages

Having the `:model_class` set to `::ContainerImage` meant that
auto_model_class was not being called, causing any records which did not
have a `:type` explicitly set by the parser would end up having a type
set to the base `::ContainerImage` class.

app/models/manageiq/providers/inventory/persister/builder/container_manager.rb

@@ -88,8 +88,6 @@ def container_images
           add_properties(
             # TODO: (bpaskinc) old save matches on [:image_ref, :container_image_registry_id]
             # TODO: (bpaskinc) should match on digest when available
-            # TODO: (mslemr) provider-specific class exists (openshift), but specs fail with them (?)
-            :model_class            => ::ContainerImage,
             :manager_ref            => %i[image_ref],
             :delete_method          => :disconnect_inv,
             :custom_reconnect_block => custom_reconnect_block