Comment 15 for bug 1903221

Configuring `sysctl` option on ceph-osd application as below fixes the issue. Thanks @corey.bryant!

```
sysctl: "{ kernel.pid_max : 2097152, vm.max_map_count : 524288, kernel.threads-max: 2097152, fs.aio-max-nr: 1048576 }"
```

I'm not sure though why specifying "fs.aio-max-nr: 1048576" explicitly is required. I'm under the impression that the parameters configured in /etc/sysctl.d/30-ceph-osd.conf should be applied in the system out of the box (e.g. by the ceph-osd charm).