provider/google: Support named_port on instance_group_manager
provider/google: Support named_port on instance_group_manager

This allows HTTP and HTTPs load-balancers to direct traffic to ports other than tcp/80 and tcp/443.

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