Be more defensive with `infping` output

[nickvanw]

Earlier today, I noticed that I wasn't collecting any stats. When I looked at the systemd output I saw:

Mar 23 12:10:20 nick-media infping[27295]: 2018/03/23 12:10:20 Pinged InfluxDB (version 1.5.0) in 316.468202ms
Mar 23 12:10:20 nick-media infping[27295]: 2018/03/23 12:10:20 Launching fping with hosts: [...]
Mar 23 12:10:21 nick-media infping[27295]: panic: runtime error: index out of range
Mar 23 12:10:21 nick-media infping[27295]: goroutine 1 [running]:
Mar 23 12:10:21 nick-media infping[27295]: main.runAndRead(0xa6e560, 0xc420142240, 0xc420122300, 0x10, 0x10, 0xa6dd60, 0xc42013a0c0, 0xc42022e780, 0x0, 0x0)
Mar 23 12:10:21 nick-media infping[27295]:         /home/nick/Go/src/github.com/nickvanw/infping/parse.go:79 +0x929
Mar 23 12:10:21 nick-media infping[27295]: main.main()
Mar 23 12:10:21 nick-media infping[27295]:         /home/nick/Go/src/github.com/nickvanw/infping/infping.go:154 +0x1491

That line would tell me that something that came back from infping was not what we were expecting - instead of ignoring it and/or logging the issue, we panic'd.

[mrngm]

If you're interested, I've tried to make parsing more robust, and added some features. Current state.