add RTT in output once it is able to detect the open port

[liw71]

Is your feature request related to a problem? Please describe.
no, not related to any issue.

Describe the solution you'd like
I have a use case, that I have a list of servers, I need to monitor RTT(round trip time) or timeout in case service is dead. Eventually, I will save this output into influxDB, and graph it on Grafana.

Describe alternatives you've considered
I have not been able to find out any alternative solution existed.

Additional context
Thanks much for looking into the PR, I am unsure if it makes sense to add it in this app at all.

[Seirdy]

rnp seems to address this.