Use persistent connections in frontend

[2opremio]

This is a workaround for Scope not showing short-lived connections properly.

With this patch and using vegeta (which uses persistent connections) instead of curl to generate some load, I get the expected visualization:

(This is a tailored local deployment, the kubernetes containers won't show in a not installation).

We will improve the tracking of short-lived connections for Scope 0.16.

[2opremio]

This is how I've run vegeta BTW:

echo "GET https://$(kubectl get service  frontend  --template '{{.spec.clusterIP}}')" | docker run --rm --name vegeta -i oba11/vegeta vegeta  attack -connections 1  -insecure -duration 0 -rate 1  > /dev/null