provider/aws: Set `storage_encrypted` to state in (#7751)
provider/aws: Set `storage_encrypted` to state in (#7751)

`aws_rds_cluster_instance`

The Import test showed that there was no setting of the
`storage_encrypted` value back to state on the Read func.

```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSRDSClusterInstance_importBasic'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
TF_ACC=1 go test ./builtin/providers/aws -v
-run=TestAccAWSRDSClusterInstance_importBasic -timeout 120m
=== RUN   TestAccAWSRDSClusterInstance_importBasic
--- PASS: TestAccAWSRDSClusterInstance_importBasic (754.30s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    754.411s
```
terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,terraform-providers/terraform-provider-aws,ClementCunin/terraform-provider-aws,Ninir/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,ashinohara/terraform-provider-aws,ashinohara/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,ashinohara/terraform-provider-aws,kjmkznr/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,nbaztec/terraform-provider-aws,ashinohara/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,charles-at-geospock/terraform-provider-aws