This is a secondary change to PR #28578
Details:
According to the [Provisioner Connection](https://www.terraform.io/docs/language/resources/provisioners/connection.html) page, provisioners require the connection block.
This change of behavior is shown prominently within a note on the [Provisioner Connection](https://www.terraform.io/docs/language/resources/provisioners/connection.html) page:
> Note: In Terraform 0.11 and earlier, providers could set default values for some connection settings, so that connection blocks could sometimes be omitted. This feature was removed in 0.12 in order to make Terraform's behavior more predictable.
However, this behavioral change is omitted from the [remote-exec provisioner](https://www.terraform.io/docs/language/resources/provisioners/remote-exec.html) page which is where a user will be if they are attempting to follow the prior behavior when this was permissible in versions prior to 0.12. This change prompts the user of that change and directs to the connection page.
Chad Bailey