[DirectBinaryAccess] AzureDataStore not chaining exceptions on upload completion

In AzureBlobStoreBackend#completeHttpUpload(), the code catches StorageException and URISyntaxException as thrown by the Azure SDK, but this exception is not chained in the DataStoreException that is thrown if those exceptions are caught, which makes it more difficult to diagnose the real issue behind the DataStoreException.

This was just a simple oversight in the original implementation.  We should also examine the other code related to direct binary access, both in the Azure and S3 implementations, to see if there are any other similar bugs.