Automatic retries during MPU with CSE breaks files

[tjcelaya]

We've discovered an issue where automatic retries triggered by the Apache HTTP Client library ruins the state of the CipherOutputStream and HmacOutputStream objects used when resending the same part. Fixing this would require snapshotting the state of the EncryptionState object in EncryptedMultipartUpload and only updating the state of encryption and digest objects if the part is uploaded successfully. Attached screenshot shows how a manually terminated request is followed by an automatic retry which corrupts the file.

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