Autoscaling using Ceilometer/Aodh in senlin

This bug tracker is for errors with the documentation, use the following as a template and remove or add fields as you see fit. Convert [ ] into [x] to check boxes:

- [x] This doc is inaccurate in this way: cpu_util is not available in ceilometer since rocky release, as it used transformers that was removed from code, so the example that uses cpu_util does not work anymore (maybe only if gnocchi reimplemented cpu_util as an aggregated metric). I suggest writing another example that uses another metric instead.
- [ ] This is a doc addition request.
- [ ] I have a fix to the document that I can paste below including example: input and output.

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Release: 6.1.0.dev80 on 2018-07-12 17:44:36
SHA: 125e403321923a727dfb5e9bc2d92aae7635cc16
Source: https://git.openstack.org/cgit/openstack/senlin/tree/doc/source/scenarios/autoscaling_ceilometer.rst
URL: https://docs.openstack.org/senlin/latest/scenarios/autoscaling_ceilometer.html