dbus: log disconnect on api and system busses

This is an interesting event. Let's log about it.

(cherry picked from commit 11ee1ba)
(cherry picked from commit c189ecc)
(cherry picked from commit 7054f66)
(cherry picked from commit d0684df)
(cherry picked from commit a88e98a)
(cherry picked from commit 7bdec4c)

Author: rpigott

src/core/dbus.c

@@ -131,10 +131,16 @@ static int signal_disconnected(sd_bus_message *message, void *userdata, sd_bus_e
         assert(message);
         assert_se(bus = sd_bus_message_get_bus(message));
 
-        if (bus == m->api_bus)
+        if (bus == m->api_bus) {
+                log_notice("Got disconnect on API bus.");
                 bus_done_api(m);
-        if (bus == m->system_bus)
+        }
+        if (bus == m->system_bus) {
+                /* If we are the system manager, this is already logged by the API bus. */
+                if (!MANAGER_IS_SYSTEM(m))
+                        log_notice("Got disconnect on system bus.");
                 bus_done_system(m);
+        }
 
         if (set_remove(m->private_buses, bus)) {
                 log_debug("Got disconnect on private connection.");