* ran ssed pattern to remove any additional ${ wrappings on variables that didn't need it.
* Removed enclosing [ from list variable inputs.
* Ran terraform-clean-syntax on project as well.
* Verrified no more failures were seen with bin/covalence ci using the latest image which contains 0.12.26 terraform.

* Updated the condition to use object path_pattern. Field definition attribute has been deprecated and produces warnings in TF12.

* Updating CHANGELOG to have new release with backward incompatabilities notes.
* Removed superfluous terraform version constraint in consul and cluster terraform files. versions.tf has the TF 0.12 constraint set there.

* Updated terraform requirement to 0.12.0 in readme.

* Updating covalence to latest version in circleci config that has terraform 0.12.26.

* Updated to use a new region for the CI executions of terraform 12 tasks.
* Updated AMI to be the latest amazonlinux 1 ecs optimized image for the us-east-1 region.
* Updated terraform bucket to use the one in us-east-1 as well.