title: GCP Custom IAM role creation with Terraform
body: <p>I'm trying to create a custom IAM role in GCP with Terraform for my instances. AFIACT, the follow should work, but yet it errors out on me, complaining that the standard roles I want to include are not valid.</p>
  
  <pre><code>resource "google_project_iam_custom_role" "my-instance-role" {
    role_id     = "myInstanceRole"
    title       = "My Instance Role"
    description = "my custom iam role"
    permissions = [
      "roles/storage.objectCreator", 
      "roles/cloudkms.cryptoKeyEncrypter"
    ]
  }
  </code></pre>
  
  <p>Here is the error message:</p>
  
  <pre><code>* google_project_iam_custom_role.my-instance-role: Error creating 
  the custom project role My Instance Role: googleapi: Error 400: 
  Permission roles/storage.objectCreator is not valid., badRequest
  </code></pre>
  
  <p>The Terraform docs aren't super clear, but from what I've read, this should work. Any idea what I'm doing wrong here? </p>