terraform/terraform_remote_state: accept complex configs
terraform/terraform_remote_state: accept complex configs

The `remote` backend config contains an attribute that is defined as a `*schema.Set`, but currently only `string` values are accepted as the `config` attribute is defined as a `schema.TypeMap`.

Additionally the `b.Validate()` method wasn’t called to prevent a possible panic in case of unexpected configurations being passed to `b.Configure()`.

This commit is a bit of a hack to be able to support this in the 0.11 series. The 0.12 series will have proper support, so when merging 0.12 this should be reverted again.

hashicorp/terraform-plugin-sdk,hashicorp/terraform-plugin-sdk