[#2180] Remove unused objects post migration

Might not actually be necessary (we don't really have
a delete feature), but just in case

lib/tasks/2018_11_29_remove_unused_openstack_objects.rake

@@ -0,0 +1,30 @@
+namespace :'2018_11_29_remove_unused_openstack_objects' do
+  task run: :environment do
+    force = (ENV['FORCE'].presence || '0').to_i != 0
+    if !force
+      rake_puts "Performing dry run, run with FORCE=1 to actually delete target objects"
+    end
+    fog_credentials = {
+      provider: 'OpenStack',
+      openstack_tenant: Rails.application.secrets.fog[:openstack_tenant],
+      openstack_api_key: Rails.application.secrets.fog[:openstack_api_key],
+      openstack_username: Rails.application.secrets.fog[:openstack_username],
+      openstack_auth_url: Rails.application.secrets.fog[:openstack_auth_url],
+      openstack_region: Rails.application.secrets.fog[:openstack_region],
+      openstack_identity_api_version: Rails.application.secrets.fog[:oopenstack_identity_api_version]
+    }
+    connection = Fog::Storage.new(fog_credentials)
+    directory = connection.directories.get(ENV['FOG_ACTIVESTORAGE_DIRECTORY'])
+    bar = RakeProgressbar.new(directory.count.to_i)
+    directory.files.each do |file|
+      if !ActiveStorage::Blob.exists?(key: file.key)
+        rake_puts "Remove unused object #{file.key}"
+        if force
+          file.destroy
+        end
+      end
+      bar.inc
+    end
+    bar.finished
+  end
+end