libpod: improve heuristic to detect cgroup

improve the heuristic to detect the scope that was created for the container.
This is necessary with systemd running as PID 1, since it moves itself
to a different sub-cgroup, thus stats would not account for other
processes in the same container.

Closes: https://github.com/containers/podman/issues/12400

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

test/e2e/systemd_test.go

@@ -109,6 +109,11 @@ WantedBy=multi-user.target
 		stats := podmanTest.Podman([]string{"stats", "--no-stream", ctrName})
 		stats.WaitWithDefaultTimeout()
 		Expect(stats).Should(Exit(0))
+
+		cgroupPath := podmanTest.Podman([]string{"inspect", "--format='{{.State.CgroupPath}}'", ctrName})
+		cgroupPath.WaitWithDefaultTimeout()
+		Expect(cgroupPath).Should(Exit(0))
+		Expect(result.OutputToString()).To(Not(ContainSubstring("init.scope")))
 	})
 
 	It("podman create container with systemd entrypoint triggers systemd mode", func() {