Add timeout if expected files don't materialize in object store

[ponyisi]

In the 3.0.1 client, we will wait indefinitely for files to show up in the S3 storage when the transformation is reported complete. We should add a timeout so that if the files don't appear within some reasonable time the client gives up and reports an error.

[ponyisi]

This is much less likely to be a problem now given that the server should not report transform complete until all outputs have been transferred to S3. However we might still consider a way of exiting the loop if we do run into some weird situation where the number of files in S3 stays less than the number reported by the transform for an extended period once the transform is complete.