Upgrade to terraform 0.12 (#394)

* run terraform upgrade tool

* fix post upgrade TODOs

* use strict typing for variables

* upgrade examples, point them at VPC module tf 0.12 PR

* remove unnecessary `coalesce()` calls

coalesce(lookup(map, key, ""), default) -> lookup(map, key, default)

* Fix autoscaling_enabled broken (#1)

* always set a value for tags, fix coalescelist calls

* always set a value for these tags

* fix tag value

* fix tag value

* default element available

* added default value

* added a general default

without this default - TF is throwing an error when running a destroy

* Fix CI

* Change vpc module back to `terraform-aws-modules/vpc/aws` in example

* Update CHANGELOG.md

* Change type of variable `cluster_log_retention_in_days` to number

* Remove `xx_count` variables

* Actual lists instead of strings with commas

* Remove `xx_count` variable from docs

* Replace element with list indexing

* Change variable `worker_group_tags` to a attribute of worker_group

* Fix workers_launch_template_mixed tags

* Change override_instance_type_x variables to list.

* Update CHANGELOG.md

.travis.yml

@@ -23,7 +23,7 @@ install:
 - bundle install
 
 before_script:
-- export TERRAFORM_VERSION=0.11.14
+- export TERRAFORM_VERSION=0.12.2
 - curl --silent --output terraform.zip "https://releases.hashicorp.com/terraform/${TERRAFORM_VERSION}/terraform_${TERRAFORM_VERSION}_linux_amd64.zip"
 - unzip terraform.zip ; rm -f terraform.zip; chmod +x terraform
 - mkdir -p ${HOME}/bin ; export PATH=${PATH}:${HOME}/bin; mv terraform ${HOME}/bin/