Fixed unreachable code warning for `cgroups::destroy`.
Fixed unreachable code warning for `cgroups::destroy`.

This was noted by coverity in CID 1462222.

Review: https://reviews.apache.org/r/72370

abudnik/mesos,Gilbert88/mesos,abudnik/mesos,dforsyth/mesos,abudnik/mesos,Gilbert88/mesos,dforsyth/mesos,reneploetz/mesos,Gilbert88/mesos,dforsyth/mesos,abudnik/mesos,abudnik/mesos,reneploetz/mesos,abudnik/mesos,dforsyth/mesos,Gilbert88/mesos,reneploetz/mesos,dforsyth/mesos,reneploetz/mesos,abudnik/mesos,reneploetz/mesos,Gilbert88/mesos,Gilbert88/mesos,reneploetz/mesos,dforsyth/mesos,Gilbert88/mesos,reneploetz/mesos,dforsyth/mesos