Fix AWS EMR Instance Group Deletion Errors
Fix AWS EMR Instance Group Deletion Errors

In situations where Terraform needs to replace an aws_emr_cluster
resource that has aws_emr_instance_group resources associated with it,
Terraform tries to execute a destroy on the instance group, but it fails
as the notion of a "destroy" on an instance group is to set the number
of instances to zero, but AWS doesn't let you modify the count of
instances in an instance group on an EMR cluster. This fixes the issue
by treating an instance group that has been terminated as no longer
existing, so Terraform won't try to execute a "destroy" and not error
out.

Fixes #1355
Fixes #9400

kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws