[proposal] Warn google_compute_instance_group without create_before_destroy

[wata727]

See https://www.terraform.io/docs/providers/google/r/compute_instance_group.html

Recreating an instance group that's in use by another resource will give a resourceInUseByAnotherResource error. You can avoid this error with a Terraform lifecycle block as outlined in the example below.

[PatMyron]

terraform-linters/tflint-ruleset-aws#202

Same thoughts on this as #23 (comment)