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

A cross build to mingw fails with:

  CC       virsystemdtest-virsystemdtest.o
../../tests/virsystemdtest.c: In function 'testCreateNoSystemd':
../../tests/virsystemdtest.c:97:9: error: implicit declaration of function 'unsetenv' [-Werror=implicit-function-declaration]
         unsetenv("FAIL_NO_SERVICE");
         ^
../../tests/virsystemdtest.c:97:9: error: nested extern declaration of 'unsetenv' [-Werror=nested-externs]

We could cop out and pull in the gnulib unsetenv module.  But when
you stop and think about it, this test requires LD_PRELOAD to work,
and systemd is a Linux-only concept anyways, both of which mean
the test could never work on mingw in the first place.  Simpler is
to just fix the test to behave like our other LD_PRELOAD tests.

* tests/virsystemdtest.c: Provide non-Linux implementation.
Signed-off-by: NEric Blake <eblake@redhat.com>

The change to query org.freedesktop.DBus.ListActivatableNames
to detect systemd broke the test suite, since we did not have
stubs to respond to this dbus call.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

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>