ephemeral_block_device isn't getting set in aws_instance resource

[ryndaniels]

As part of fixing #7198, we discovered that ephemeral_block_device doesn't actually get set in the aws_instance resource. We'll want to actually do that, as this is likely the cause of several existing issues and bug reports related to ephemeral_block_devices.

[ryndaniels]

After digging further, it seems like neither BlockDeviceMappings nor DescribeVolumes surfaces ephemeral block device information. Ephemeral block device info for running instances can be found by querying instance metadata but that feels a bit hacky.

The BlockDeviceMapping struct does have a VirtualName field for ephemeral devices, but in our acceptance testing, that field was nil for all devices returned this way, even though there was an ephemeral device configured in the test setup - ephemeral devices seem to be an input-only sort of thing.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!