The problem is described by [0] but its effect on libvirt is that
starting a container with a full distro running systemd after having
stopped it simply fails.

The container cleanup now calls the machined Terminate function to make
sure that everything is in order for the next run.

 [0]: https://bugs.freedesktop.org/show_bug.cgi?id=68370

https://bugzilla.redhat.com/show_bug.cgi?id=1008619

1,003 bytes in 1 blocks are definitely lost in loss record 599 of 635
==404== by 0x50728A7: virBufferAddChar (virbuffer.c:185)
==404== by 0x50BC466: virSystemdEscapeName (virsystemd.c:67)
==404== by 0x50BC6B2: virSystemdMakeSliceName (virsystemd.c:108)
==404== by 0x50BC870: virSystemdCreateMachine (virsystemd.c:169)
==404== by 0x5078267: virCgroupNewMachine (vircgroup.c:1498)

This patch introduces virDBusIsServiceEnabled, we can use
this method to get if the service is supported.

In one case, if org.freedesktop.machine1 is unavailable on
host, we should skip creating machine through systemd.
Signed-off-by: NGao feng <gaofeng@cn.fujitsu.com>

On hosts that don't have the DBus service running or installed the new
systemd cgroups code failed with hard error instead of falling back to
"manual" cgroup creation.

Use the new helper to check for the system bus and use the fallback code
in case it isn't available.

There are some interesting escaping rules to consider when dealing
with systemd slice/scope names. Thus it is helpful to have APIs
for formatting names
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

If systemd machine does not exist, return -2 instead of -1,
so that applications don't need to repeat the tedious error
checking code
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

To register virtual machines and containers with systemd-machined,
and thus have cgroups auto-created, we need to talk over DBus.
This is somewhat tedious code, so introduce a dedicated function
to isolate the DBus call in one place.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>