Commit e865faf adds visual indentation for diagnostic messages using various
vertical line characters. The present commit disables this behaviour when
running with colourised output disabled.
While the contents of stderr are not intended to be part of the Terraform API,
this is currently how the hashicorp/terraform-exec library detects certain
error types in order to present them as well-known Go errors to the user. Such
detection is complicated when vertical lines are added to the CLI output at
unpredictable points.
I expect this change will also be helpful for screen reader users.