description is now a required field for google_dns_managed_zone
description is now a required field for google_dns_managed_zone

The description field for a managed-zone is now a required field when using the Cloud API.
This commit defaults the field to use the text "Managed by Terraform" to minimize required boilerplate for Terraform users.

Ref: https://cloud.google.com/sdk/gcloud/reference/dns/managed-zones/create

selmanj/terraform-provider-google,hashicorp/terraform-provider-google-beta,hashicorp/terraform-provider-google-beta,ubschmidt2/terraform-provider-google,hashicorp/terraform-provider-google-beta,nickithewatt/terraform-provider-google,drebes/terraform-provider-google,hashicorp/terraform-provider-google-beta,nickithewatt/terraform-provider-google,terraform-providers/terraform-provider-google,hashicorp/terraform-provider-google,hashicorp/terraform-provider-google,nickithewatt/terraform-provider-google,selmanj/terraform-provider-google,selmanj/terraform-provider-google,ubschmidt2/terraform-provider-google,terraform-providers/terraform-provider-google,drebes/terraform-provider-google,rosbo/terraform-provider-google,ubschmidt2/terraform-provider-google,hashicorp/terraform-provider-google,terraform-providers/terraform-provider-google,terraform-providers/terraform-provider-google,ubschmidt2/terraform-provider-google,rosbo/terraform-provider-google,drebes/terraform-provider-google,terraform-providers/terraform-provider-google,rosbo/terraform-provider-google,drebes/terraform-provider-google,rosbo/terraform-provider-google,hashicorp/terraform-provider-google