Metric gathering make Logstash 5 crash at startup when procfs is not mounted

I just installed logstash5[1] on a FreeBSD 10[2] system. Logstash startup fails due to unmounted procfs:

```
OperatingSystemImpl.java:-2:in `getCommittedVirtualMemorySize': java.lang.InternalError: errno: 2 error: Unable to open /proc/curproc/map
```

For security reasons we can't mount the procfs. Is there any solution for this? procfs wasn't required in logstash version 2.3.2.

[1] Logstash
Version: `logstash5-5.0.0 `

[2] FreeBSD
Version: `FreeBSD 10.3-RELEASE-p12`