Description of problem:
"virsh shutdown" stop all process inside container, but "virsh list" report that container still running. After restart libvirt, container get correct status "shut off"

Version-Release number of selected component (if applicable):
5.0.0-1.el7.x86_64

How reproducible:
see later

Steps to Reproduce:
1. create lxc container LXC_NAME
2. virsh start LXC_NAME, check "virsh list" output
3. virsh shutdown LXC_NAME, check "virsh list" output

Actual results:
container LXC_NAME hav status "running"

Expected results:
container LXC_NAME must have status "shut off"

Additional info:
libvirt-5 can work with cgroups controller v1 and v2. On Centos-7.6
libvirt correct detect that only one controller v1 available.
When container stopped, inside virLXCProcessStop() call next code:
 if (priv->cgroup) {
        rc = virCgroupKillPainfully(priv->cgroup);
        if (rc < 0)
            return -1;
        if (rc > 0) {
            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                           _("Some processes refused to die"));
            return -1;
        }

And because virCgroupKillPainfully() return -1, label "cleanup" never reached:
 cleanup:
    virLXCProcessCleanup(driver, vm, reason);

Function virCgroupKillPainfully() call virCgroupKillRecursive() and it return -1, because check only variable backends[i] before call method associated with current backend. But even cgroups v2 not detected, member of array backends[1] still present. Then we call backends[i]->killRecursive(group, signum, pids) and it return -1.
I prepare patch by analogy with other places of code, where used cgroups backend functions:

diff -urN libvirt-5.0.0/src/util/vircgroup.c libvirt-5.0.0.patch/src/util/vircgroup.c
--- libvirt-5.0.0/src/util/vircgroup.c  2019-01-10 23:35:29.005474054 +0300
+++ libvirt-5.0.0.patch/src/util/vircgroup.c    2019-02-25 18:07:56.394307749 +0300
@@ -2622,7 +2622,7 @@
     }
 
     for (i = 0; i < VIR_CGROUP_BACKEND_TYPE_LAST; i++) {
-        if (backends[i]) {
+        if (backends[i] && backends[i]->available()) {
             rc = backends[i]->killRecursive(group, signum, pids);
             if (rc < 0) {
                 ret = -1;

Tested on centos-7.6, now container shutdowned correctly, virsh list report "shut off"