Chunked Box uploader should be made fault-tolerant like the older uploader is

[ressy]

I'd left the fault-tolerant logic in place only for the older Box upload method for small files (that uses folder.upload) but not the newer chunked version (that uses folder.create_upload_session()), but I'm still seeing occasional instances of requests.exceptions.ConnectionError when a connection is interrupted mid-upload. I don't see any reason not to apply the same retry structure around both upload types.