title: terraform plan returns the Error: Unsupported argument
body: <p>I have the following three files as below:
  main.tf, variables.tf and dev.auto.tfvars</p>
  
  <p>Snippet from <strong>main.tf</strong></p>
  
  <pre><code>module "sql_vms" {
    source                  = "git::git@github.com:xxxxxxxxxxxx/terraform-modules//azure/"
    rg_name                 = var.resource_group_name
    location                = module.resource_group.external_rg_location
    vnet_name               = var.virtual_network_name
    subnet_name             = var.sql_subnet_name
    app_nsg                 = var.application_nsg
    vm_count                = var.count_vm
    base_hostname           = var.sql_host_basename
    sto_acc_suffix          = var.storage_account_suffix
    vm_size                 = var.virtual_machine_size
    vm_publisher            = var.virtual_machine_image_publisher
    vm_offer                = var.virtual_machine_image_offer
    vm_sku                  = var.virtual_machine_image_sku
    vm_img_version          = var.virtual_machine_image_version
    username                = var.username
    password                = var.password
  }
  </code></pre>
  
  <p>Snippet from <strong>variables.tf</strong></p>
  
  <pre><code>variable "app_subnet_name" {
    type    = string
  }
  
  variable "sql_subnet_name" {
    type    = string
  }
  </code></pre>
  
  <p>Snippet from <strong>dev.auto.tfvars</strong></p>
  
  <pre><code>app_subnet_name = "subnet_1"
  
  sql_subnet_name = "subnet_2"
  
  application_nsg = "test_nsg"
  </code></pre>
  
  <p>However, I'm getting error like below</p>
  
  <pre><code>Error: Unsupported argument
  
    on main.tf line 7, in module "sql_vms":
     7:   subnet_name    = var.sql_subnet_name
  
  An argument named "subnet_name" is not expected here.
  
  
  Error: Unsupported argument
  
    on main.tf line 8, in module "sql_vms":
     8:   app_nsg        = var.application_nsg
  
  An argument named "app_nsg" is not expected here.
  </code></pre>
  
  <p>My modules directory structure looks like below</p>
  
  <pre><code>$ ls -R terraform-modules/
  terraform-modules/:
  aws  azure  gcp
  
  terraform-modules/aws:
  alb  ec2-instance-rhel
  
  terraform-modules/aws/alb:
  
  terraform-modules/aws/ec2-instance-rhel:
  main.tf
  
  terraform-modules/azure:
  compute  resourcegroup  sqlserver
  
  terraform-modules/azure/compute:
  main.tf  README.md  variable.tf
  
  terraform-modules/azure/resourcegroup:
  data.tf  outputs.tf  variables.tf
  
  terraform-modules/azure/sqlserver:
  main.tf  README.md  variables.tf
  
  terraform-modules/gcp:
  compute
  
  terraform-modules/gcp/compute:
  main.tf
  </code></pre>
  
  <p>Any idea what is going wrong here?</p>