This commit adds tests to verify the behavior of the S3BlobContainer and
its underlying AWS SDK client when the remote S3 service is responding
errors or not responding at all. The expected behavior is that requests are
retried multiple times before the client gives up and the S3BlobContainer
bubbles up an exception.
The test verifies the behavior of BlobContainer.writeBlob() and
BlobContainer.readBlob(). In the case of S3 writing a blob can be executed
as a single upload or using multipart requests; the test checks both scenario
by writing a small then a large blob.
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