Bug 989706: Quiet extra output from Libcgroup.usage

https://bugzilla.redhat.com/show_bug.cgi?id=989706

Added option to `oo_spawn` that silences output when logged to
`NodeLogger`. Output will now appear like:

```
July 30 11:30:00 INFO Shell command 'grep -H "" */{cpu.stat,cpuacct.usage,cpu.cfs_quota_us} 2> /dev/null' ran. rc=0 out=<silenced>
```

Also added custom logger for cgroups information, which is used [here][1]

[1]: https://github.com/openshift/li/pull/1782