Have "ensure_idempotent" Field to be True by Default

[najose]

In most of the use cases, users would expect the Terraform plan to be always idempotent except in cases where a module might create/modify/delete resources based on dynamically changing factors. In such exceptional cases users should set ensure_idempotent to false.

[najose]

Implementing this probably won't be trivial due to how Go works combined with how mapstructure works.

Relevant: mitchellh/mapstructure#111

Or just renaming the field so it implies it's idempotent by default. 😄