test(storage): fix s3_sdk test flake (#2295)
test(storage): fix s3_sdk test flake (#2295)

Add retry for HMAC Key test creation. The client no longer retries
this operation automatically because it is non-idempotent.

Fixes #2292
GoogleCloudPlatform/golang-samples,GoogleCloudPlatform/golang-samples,GoogleCloudPlatform/golang-samples