Retry on Network Timeout

I was having some issues with the SDK not respecting the maxRetryCount I specified in the AWSServiceConfiguration and the session manager not retrying on network timeout. I found in the copyWithzone method, maxRetryCount was not getting carried over so the copies would always have a maxRetryCount of 0, causing it to never retry. Also, in the case where the response is completely lost, the session task response is nil, which always fails the isKindOfClass check, which prevents any retries. I've tested these changes on s3 file uploads and it works as intended.