title: Terraform not finding third party plugin in directory specified for plugins
body: <p>Attempting to get Terraform to work on windows 10 64 bit, using the Virtualbox provider plugin listed here (<a href="https://github.com/terra-farm/terraform-provider-virtualbox" rel="nofollow noreferrer">https://github.com/terra-farm/terraform-provider-virtualbox</a>). I've verified that the plugin exists in %APPData%/terraform.d/plugins/windows_amd64 but it says it's not there. Have tried the following with no luck</p>
  
  <ul>
  <li>Tried copying terraform.d to local instead of roaming for %APPData%.</li>
  <li>Tried in the root directory where the terraform executible exists</li>
  <li>Tried just the virtualbox folder instead of the entire plugin in both %APPData% locations </li>
  <li>Tried in the folder where the terraform files exists</li>
  </ul>
  
  <p>None have worked. It acts as if the folder it says to place the plugin, and where it's looking are mismatched, but I doubt something like that would have made it to release, so I'm at a loss as to why it's not seeing the plugin.</p>
  
  <p>Terraform is the latest version. Using the following in my example.tf (the only tf file in the directory that i execute terraform form)</p>
  
  <pre><code>resource "virtualbox_vm" "node" {
    count     = 2
    name      = format("node-%02d", count.index + 1)
    image     = "https://app.vagrantup.com/ubuntu/boxes/bionic64/versions/20180903.0.0/providers/virtualbox.box"
    cpus      = 2
    memory    = "512 mib"
    user_data = file("user_data")
  
    network_adapter {
      type           = "hostonly"
      host_interface = "vboxnet1"
    }
  }
  
  output "IPAddr" {
    value = element(virtualbox_vm.node.*.network_adapter.0.ipv4_address, 1)
  }
  
  output "IPAddr_2" {
    value = element(virtualbox_vm.node.*.network_adapter.0.ipv4_address, 2)
  }
  </code></pre>