D-bus introduced some changes in its locking code. Overriding the init
function skips the new locking init and thus crashes later in libvirt
test. Removing the function makes the test pass again.

Coverity complains that the test suite did not check the
return value of dbus_message_iter_append_basic() as we did
in most other places.
Signed-off-by: NDaniel P. Berrange <berrange@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>

Ubuntu libdbus.so links with -Bsymbolic-functions, which means
that we can only LD_PRELOAD functions that we directly call.
Functions which libdbus.so calls internally can not be replaced.
Thus we cannot use dbus_message_new_error or dbus_message_new_method_return
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

On RHEL 5, with dbus 1.1.2, compilation failed with:

virsystemdmock.c: In function 'dbus_connection_send_with_reply_and_block':
virsystemdmock.c:68: warning: implicit declaration of function 'dbus_message_set_serial'

Fix this by instead bypassing all attempts to use a dbus serial.

* tests/virsystemdmock.c (dbus_message_set_reply_serial): Add new
override.
(dbus_connection_send_with_reply_and_block): No longer bother with
the serial.
Signed-off-by: NEric Blake <eblake@redhat.com>

A cross-compile to mingw failed:

  CC       virsystemdmock_la-virsystemdmock.lo
../../tests/virsystemdmock.c:29:6: error: 'dbus_connection_set_change_sigpipe' redeclared without dllimport attribute: previous dllimport ignored [-Werror=attributes]
 void dbus_connection_set_change_sigpipe(dbus_bool_t will_modify_sigpipe ATTRIBUTE_UNUSED)
      ^

But when you think about it, systemd is Linux-only, and even our
use of LD_PRELOAD to provide mock syscalls is Linux-only.

* tests/virsystemdmock.c: Avoid compilation outside Linux.
Signed-off-by: NEric Blake <eblake@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>