Correct template path and metadata path in quick start

template path `elements/nova/os-config-applier' and metadata path
`elements/boot-stack/config.json' do not exist anymore in latest
`tripleo-image-elements' project. A workable quick start is
essentially important for beginners, so correct the two places.

Change-Id: I7d55a4c6766031d85e3a8ea1ba3a2afb2f802f46