[Heartbeat] Rootless ping doesn't work on OSX

We have a report from @josephPresseller that rootless ping on OSX doesn't work. It appears to produce documents with errors like:

```
"error": {
"type": "io",
"message": "write udp 0.0.0.0:0->172.217.8.174: invalid argument"
},
```

which indicate that we're trying a rootless ping but don't have perms. Running as root fixes this, but we can do better on OSX, and should instead fail to start, giving a permissions error.