Bug 989706: Throttler dies if no cgroups are present

https://bugzilla.redhat.com/show_bug.cgi?id=989706

If there were no cgroups present, the `grep` command would fail.
By not expecting a 0 exit status, we can silently ignore this problem.
Merge pull request #3242 from fotioslindiakos/Bug989706

Merged by openshift-bot