Move elasticsearch create to deployments API

[marclop]

Overview

ecctl elasticsearch create allows both the creation of a simple Elasticsearch cluster and of a complex sliders-able clustere with a more complex topology. There's a number of problems with the APIs and the way that command operates:

1. Uses POST /v1/clusters/elasticsearch to create it, which we should move away from since it'll soon be deprecated.
2. Uses the legacy cluster plan definition, which works OK today, but there's no assurance it will continue to work going forward since there's a bunch of fields used in the models to create it which are clearly marked as deprecated.