[Feature Request] - Enable deep_check via Environment Variable

[brendanjerwin]

I'd like to only enable the deep_check feature when running tflint in CI so that I'm not forced to have AWS credentials on any workstation being used to edit .tf files.

Perhaps:

export TFLINT_AWS_DEEP_CHECK=1

[brendanjerwin]

In our shop, we don't allow the credentials used by Terraform to be used on workstations. But I'd still like to have tflint integrated with my editor. As it is, I can't use the deep_check feature and editor integration because it just barfs when it can't find credentials.