provider/google: Improve backend service error handling
provider/google: Improve backend service error handling

Unset id in case the backend service cannot be created. This basically
updates these lines of code to match the more modern style which is
being used e.g. for the google_compute_instance resource.

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