provider/aws: Prevent users from mixing top-level and nested EBS volume declarations at validate stage

[catsby]

Users should not be able to both specify any ebs_block_devices in an instance, as well as have that instance included in a volume_attachment resource.

Doing so causes a plan/refresh loop, due to the conflicting count of EBS Block devices.

See #3262 as an example

[gtmtech]

@catsby Is there any chance of making terraform so that these CAN co-exist.

Its useful to be able to have one ebs volume with delete_on_termination, and one without.

Either that or the aws_volume_attachment resource needs a delete_on_termination too, so if the instance is removed, it propagates to removing the volume too.

[mitchellh]

Hey @catsby, closing this since we're not working on it atm and I actually do believe there are enhancement requests for a global validation function. We'll leave it at that for now.

[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.

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