tests: force dbus-daemon to generate an abstract socket
dbus 1.14.4 changed the behavior of unix:tmpdir to be equivalent to unix:dir, which cases dbus-daemon to generate path based sockets, instead of the previous abstract sockets. [1] In this change we force dbus-daemon to generate an abstract socket by specifying the abstract socket address in the command.
[1] https://gitlab.freedesktop.org/dbus/dbus/-/blob/dbus-1.14/NEWS#L64