Replace occurrences of list_join with Fn::Join

Replace occurrences of list_join with Fn::Join

When change I6730ffe1e27d952d563c16a9480298fbef9f61fe got merged we
introduced some occurrences of list_join which should have been
migrated to Fn::Join (change I039f57ab39c1fcfc319a7a34265ba4fabf4ccd08)

This caused overcloud CI jobs to fail with:
Property error : allNodesConfig: config Items to join must be strings

This change fixes this by replacing newly introduced occurrences
of list_join with Fn::Join

Change-Id: Ibac193781d31d6f81e955e7b9381e13cfdd0ab1d