provider/aws: Fix root-block-device bug
provider/aws: Fix root-block-device bug

Previously the `root_block_device` config map was a `schema.TypeSet` with an empty `Set` function, and a hard-limit of 1 on the attribute block.
This prevented a user from making any real changes inside the attribute block, thus leaving the user with a `Apply complete!` message, and nothing changed.

The schema API has since been updated, and we can now specify the `root_block_device` as a `schema.TypeList` with `MaxItems` set to `1`. This fixes the issue, and allows the user to update the `aws_instance`'s `root_block_device` attribute, and see changes actually propagate.

ashinohara/terraform-provider-aws,ashinohara/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,Ninir/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,nbaztec/terraform-provider-aws,Ninir/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,ClementCunin/terraform-provider-aws,kjmkznr/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,nbaztec/terraform-provider-aws,Ninir/terraform-provider-aws,ClementCunin/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,nbaztec/terraform-provider-aws,ashinohara/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,ashinohara/terraform-provider-aws,ClementCunin/terraform-provider-aws