fix or remove set_keep_alive_whitespace_interval

[nadavMiz]

Environment info

• NooBaa Version: VERSION
• Platform: Kubernetes 1.14.1 | minikube 1.1.1 | OpenShift 4.1 | other: specify

currently when complete_multipart_upload takes too long we send headers to show progress to the cluster, to prevent the client from closing the connection. since we send the headers to keep the connection, we can't write new headers (we get error ERR_HTTP_HEADERS_SENT). currently this happens for version-id and encryption. since we only link the file and don't really copy it, complete multipart upload should not take that long. it should only happen in case on problems with the file system that make the command take a lot of time (see #8524). we should decide if we want to remove set_keep_alive_whitespace_interval function, or to fix it in case we want to keep it

original keep alive issue: #6591. this PR was originally added when we copied the parts, and complete multipart upload time was relative to the file size

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