Fix issues with ES node replacement documentation

[zackkrida]

The ES node replacement doc has a few issues I need to fix:

• <env> is used in multiple contexts which accept different values (staging in some places, dev in others, for example)
• Inconsistency with usage of j tf versus terraform in places. I think we should stick to using plain terraform while CD-ed into the correct directory, and note such in the instructions.
• Step 8 forgets to include the -<env>- section of the elasticsearch module name(s), which could confuse someone implementing the plan.
• Critical Step 3 brushes over the terraform plan/apply step, despite this step needing to be a targeted apply in our old terraform state. Applying a non-target state change here could be disaster.
• Nit: incorrect "ElasticSearch" capitalization in places