Add ICMP duration metrics

[SuperQ]

Add a gauge to measure various parts of the ICMP probe.

Fixes: #315

[brian-brazil]

This needs updating

[SuperQ]

Whups, copy-pasta. :)

[SuperQ]

I did some testing, the Go ICMP code seems way slower than the normal C ping program. For example, over my local ethernet:

10 packets transmitted, 10 received, 0% packet loss, time 9218ms
rtt min/avg/max/mdev = 0.312/0.354/0.396/0.031 ms

With the blackbox_exporter:

probe_icmp_duration_seconds{phase="rtt"} 0.000537164
probe_icmp_duration_seconds{phase="rtt"} 0.000538153
probe_icmp_duration_seconds{phase="rtt"} 0.000447007
probe_icmp_duration_seconds{phase="rtt"} 0.00060231
probe_icmp_duration_seconds{phase="rtt"} 0.000539882
probe_icmp_duration_seconds{phase="rtt"} 0.000630896
probe_icmp_duration_seconds{phase="rtt"} 0.000521305
probe_icmp_duration_seconds{phase="rtt"} 0.000569541
probe_icmp_duration_seconds{phase="rtt"} 0.000598364
probe_icmp_duration_seconds{phase="rtt"} 0.000574883

Go seems to add about 200us to the ping time. (average 556us)

This is still far more accurate than the full probe_duration_seconds.

probe_duration_seconds 0.001279944
probe_duration_seconds 0.000909941
probe_duration_seconds 0.000842068
probe_duration_seconds 0.000947099
probe_duration_seconds 0.000957239
probe_duration_seconds 0.001390443
probe_duration_seconds 0.001156965
probe_duration_seconds 0.001060642
probe_duration_seconds 0.00130084
probe_duration_seconds 0.0013451

[SuperQ]

FYI, Travis is failing due to Go 1.11 go fmt.

[baiwfg2]

@brian-brazil @SuperQ Does probe_icmp_duration_seconds exist in current version ? I don't see it in prometheus metric list:

[c0dyhi11]

@brian-brazil @SuperQ Does probe_icmp_duration_seconds exist in current version ? I don't see it in prometheus metric list:

Same here...

[zhangzheng1019]

@SuperQ @brian-brazil Similarly, I don’t have an ICMP indicator here.