provider/aws: Fixes #5108 (launch_configuration failures)

[pforman]

Fixes #5108 - Invalid address to set: []string{"root_block_device", "0", "encrypted"}

Fixes the problem where the root_block_device could cause an apply error by reading back an "encrypted" parameter that was meant for an ebs_block_device. "encrypted" is not part of the root_block_device schema, since it can't be set explicitly.

Added a check in Create to fail when the root device is incorrectly specified as an ebs_block_device, as this causes continual refreshing due to mismatched state between root_block_device and ebs_block_device.

I wish I could make this trigger during plan, but it doesn't, only on apply. I think that's an improvement over refresh-looping.

"encrypted" and "snapshot_id" should be guarded by ConflictsWith, but that doesn't appear to work on nested resources despite #1926. I tried it and then reverted that when I saw no effect.

I think this PR as-is is an improvement over the current state of surprise failures. Any advice about the two issues above would be greatly appreciated, though. They're not blocking bugs, but would help prevent further surprises and questions.

[nickm4062]

Any update on this patch?

[catsby]

Thanks for the fix, @pforman ! I check this out to verify things and it looks good here. Verified the existing tests pass:

TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSLaunchConfiguration_ -timeout 120m
=== RUN   TestAccAWSLaunchConfiguration_importBasic
--- PASS: TestAccAWSLaunchConfiguration_importBasic (9.66s)
=== RUN   TestAccAWSLaunchConfiguration_basic
--- PASS: TestAccAWSLaunchConfiguration_basic (18.86s)
=== RUN   TestAccAWSLaunchConfiguration_withBlockDevices
--- PASS: TestAccAWSLaunchConfiguration_withBlockDevices (11.15s)
=== RUN   TestAccAWSLaunchConfiguration_withSpotPrice
--- PASS: TestAccAWSLaunchConfiguration_withSpotPrice (11.09s)
=== RUN   TestAccAWSLaunchConfiguration_withIAMProfile
--- PASS: TestAccAWSLaunchConfiguration_withIAMProfile (21.11s)
=== RUN   TestAccAWSLaunchConfiguration_withEncryption
--- PASS: TestAccAWSLaunchConfiguration_withEncryption (11.57s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    83.460s
Test:
[github.com/hashicorp/terraform][pr-6512](2)$

[ghost]

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