Add distributed tracing to Computations

We need to have measure of latency and throughput for a computations dag.
This can be done by sampling (some record are instrumented to get timestamp of each step).
Could be also interesting to see how a distributed tracing system can be used like zipkin.
http://concord.io/docs/tutorials/metrics.html
or https://github.com/opentracing/opentracing-java

or https://github.com/jaegertracing/jaeger