Reorganizing render, deploy, destroy to unify stages input_vars, tf_objects, checks, and state_imports

[costrouc]

This PR is only a refactor of render, deploy, and destroy. The motivation for this is allowing for the closing of #1081. In order to properly delete the aws ingress we need to be able to get the terraform outputs from some early kubernetes stages. This PR will also allow for the easier transition to #865.

There are no modifications to the behavior of the code.

Going into more detail about the heart of the issue:

For each stage we have to supply input variables, dymanic terraform objects, terraform imports.

We cannot run terraform output without supplying the proper input variables. Within deploy.py and destroy.py this was becoming repetative. Thus I've moved the definitions into a stages/*.py directory which will need to be done with whatever extension mechanism we chose.

[danlester]

This is a great step forward!

At some point maybe we will refactor using classes to enforce the structure and reduce repetition of strings such as stages/03-kubernetes-initialize.