Myiac faild after terraform version upgrade

[bartlomiejsawicki]

Myiac can't detect change of terraform version. When run on old tfstate terraform ask to run upgrade command but myiac faild by not taking any action.

Steps to reproduce the behavior:

1. Build env with terraform 0.12 and remote state enabled
2. Upgrade terraform in dev image to 0.15
3. rm .terraform from code directory (cause by bug Myiac failed when terraform init needed #81)
4. Run destroy or create cluster
5. Terraform will complain about terraform upgrade command which should be used to upgrade remote state

Myiac detect message about required upgrade and run it or has possibility to do it manually.