Change order of parsing so that include is parsed first

[yorinasub17]

This is a fix for #814 (comment). Specifically, right now due to the parsing order get_parent_terragrunt_dir does not work in locals. This breaks usage of locals to refactor out a path calculation that depends on the parent dir, such as getting a default empty.yml file in the workaround for merging in optional variables from the directory hierarchy.

Note that this is a backwards incompatible change, where you can no longer reference locals in include. However, this is probably a worthy tradeoff where we are trading the not so useful function of referencing locals in include blocks (which will in 80% of use cases be find_in_parent_folders()) with the ability to use include dependent functions in the parent locals.

[yorinasub17]

Merging this in. Thanks for review!