bugfix/terraform 12 var-file suffix

[jschoewe]

After upgrading to Terraform 12, I was getting the following error when running plan/apply:

Error: Argument or block definition required

  on /tmp/tmpcSY9YL line 1:
   1: <input variables dict>

An argument or block definition is required here.

After more testing I found that Terraform 12 no longer accepts variable definition files without an extension. This change fixes that problem and has no effect on Terraform versions < 12.

https://www.terraform.io/docs/configuration/variables.html#variable-definitions-tfvars-files

Steps to reproduce this problem:

1. Upgrade to Terraform 12 (still in Beta)
   https://www.terraform.io/upgrade-guides/0-12.html
2. Save a json object in a file with no extension
3. Run terraform plan with that var-file as an input

[beelit94]

nice work, thank you @jschoewe