Fix ipv6 prefix detection with aws-sdk-go-v2

[rifelpet]

AWS ipv6 jobs have been failing with this nodeup error:

Sep 05 03:58:28 i-002abc28507b7ab4f nodeup[4374]: I0905 03:58:28.588344    4374 executor.go:171] Continuing to run 1 task(s)
Sep 05 03:58:38 i-002abc28507b7ab4f nodeup[4374]: I0905 03:58:38.589379    4374 executor.go:113] Tasks: 182 done / 199 total; 1 can run
Sep 05 03:58:38 i-002abc28507b7ab4f nodeup[4374]: I0905 03:58:38.589427    4374 executor.go:214] Executing task "Prefix/prefix": Prefix: prefix
Sep 05 03:58:38 i-002abc28507b7ab4f nodeup[4374]: W0905 03:58:38.592417    4374 executor.go:141] error running task "Prefix/prefix" (6m1s remaining to succeed): failed to get "network/interfaces/macs/06:05:2f:0e:c6:eb/ipv6-prefix" from ec2 meta-data: operation error ec2imds: GetMetadata, http response error StatusCode: 404, request to EC2 IMDS failed
Sep 05 03:58:38 i-002abc28507b7ab4f nodeup[4374]: I0905 03:58:38.592440    4374 executor.go:171] Continuing to run 1 task(s)
Sep 05 03:58:48 i-002abc28507b7ab4f nodeup[4374]: I0905 03:58:48.593316    4374 executor.go:113] Tasks: 182 done / 199 total; 1 can run
Sep 05 03:58:48 i-002abc28507b7ab4f nodeup[4374]: I0905 03:58:48.593367    4374 executor.go:214] Executing task "Prefix/prefix": Prefix: prefix
Sep 05 03:58:48 i-002abc28507b7ab4f nodeup[4374]: W0905 03:58:48.596224    4374 executor.go:141] error running task "Prefix/prefix" (5m51s remaining to succeed): failed to get "network/interfaces/macs/06:05:2f:0e:c6:eb/ipv6-prefix" from ec2 meta-data: operation error ec2imds: GetMetadata, http response error StatusCode: 404, request to EC2 IMDS failed

This occurs in the task's Find method. We should just return nil (indicating the resource doesn't exist yet and needs to be created) but there was a bug in the error handling in aws-sdk-go-v2 and we weren't identifying the request as a 404.

The SDK's IMDS client uses different error types from normal services, so we have to unwrap the error differently:

https://github.com/aws/aws-sdk-go-v2/blob/f1d71c59a1499981873f70db8c92d07242779670/feature/ec2/imds/request_middleware.go#L185-L191

Once we confirm this fixes all of the failing ipv6 jobs then we should cherrypick this to 1.30

[k8s-ci-robot]

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This pull-request has been approved by: hakman

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[rifelpet]

/retest