node spec: add rubygem(json)
Bug 1077077

`oo-cgroup-read` needs rubygem-json to run (see related bugs 924556 and
912215)
Check for pid existence in graceful shutdown func

Check for the existence of the given pid before trying to
perform commands on it during graceful shutdowns.

Resolve bug https://bugzilla.redhat.com/show_bug.cgi?id=1081020
Merge pull request #5066 from dobbymoodge/BZ1077077

Merged by openshift-bot
Merge pull request #5075 from ironcladlou/force-stop-fix

Merged by openshift-bot