output service_account_email_address

[jsirianni]

I need to give the cloud sql service account access to a GCS bucket, like this:

resource "google_storage_bucket_iam_binding" "bucket" {
 role   = "roles/storage.objectCreator"
 bucket = google_storage_bucket.bucket.name

 members = [
  "serviceAccount:${module.mydatabase.service_account_email_address}"
 ]
}

I did not add tests, as not all outputs appear to be tested. I can add test cases if required. The existing test suite passes.

Currently I am using my fork with success.

[yorinasub17]

The test failed for a different reason unrelated to this PR, so will go ahead and merge and release this. Thanks!