<oo-cgroup-read> bug 924556 pull in native rubygem-open4

oo-cgroup-read was changed from env ruby to /usr/bin/ruby due to
selinux issues (https://bugzilla.redhat.com/show_bug.cgi?id=901449).
Then the implementation was changed from one using cgget to one
using rubygem open4 due to selinux issues
(https://bugzilla.redhat.com/show_bug.cgi?id=912215)
But native rubygem(open4) was not listed as a dependency now that
ruby 1.9.3 is the standard. So, modifying the spec file to ensure
it is present on every system, to prevent JBoss build failures
(https://bugzilla.redhat.com/show_bug.cgi?id=924556)