Terraform 0.12 support

[disaac]

• Updated circleci and covalence to use unifiouat account.
• Updated values to use default vpc/subnets/sgs from new account.
• Updated covalence launcher script.
• Convert to bool values to support latest provider using local vars.
• Remove superfluous terraform version statements in modules.
• Add complete stack to covalence test environments for local testing.
• Provide nulls instead of empty strings on bool required values.
• Upate region specific AMI values for linux AMI in us-east-1 since this was changed.
• Create new SSH key and add to unifiouat account. Add AWS cli command to comments for reference.
• Updated to version 0.4.0 in changelog to prepare for Merge.