systemd: don't report an error if the guest is already terminated

In many cases where we invoke virSystemdTerminateMachine the
process(es) will have already gone away on their own accord.
In these cases we log an error message that the machine does
not exist. We should catch this particular error and simply
ignore it, so we don't pollute the logs.

src/util/virsystemd.c

@@ -338,18 +338,22 @@ int virSystemdTerminateMachine(const char *name,
     int ret;
     DBusConnection *conn;
     char *machinename = NULL;
+    virError error;
+
+    memset(&error, 0, sizeof(error));
 
     ret = virDBusIsServiceEnabled("org.freedesktop.machine1");
     if (ret < 0)
-        return ret;
+        goto cleanup;
 
     if ((ret = virDBusIsServiceRegistered("org.freedesktop.systemd1")) < 0)
-        return ret;
+        goto cleanup;
+
+    ret = -1;
 
     if (!(conn = virDBusGetSystemBus()))
-        return -1;
+        goto cleanup;
 
-    ret = -1;
     if (!(machinename = virSystemdMakeMachineName(name, drivername, privileged)))
         goto cleanup;
 
@@ -366,7 +370,7 @@ int virSystemdTerminateMachine(const char *name,
     VIR_DEBUG("Attempting to terminate machine via systemd");
     if (virDBusCallMethod(conn,
                           NULL,
-                          NULL,
+                          &error,
                           "org.freedesktop.machine1",
                           "/org/freedesktop/machine1",
                           "org.freedesktop.machine1.Manager",
@@ -375,9 +379,18 @@ int virSystemdTerminateMachine(const char *name,
                           machinename) < 0)
         goto cleanup;
 
+    if (error.code == VIR_ERR_ERROR &&
+        !STREQ_NULLABLE("org.freedesktop.machine1.NoSuchMachine",
+                        error.str1)) {
+        virReportErrorObject(&error);
+        goto cleanup;
+    }
+
     ret = 0;
 
  cleanup:
+    virResetError(&error);
+
     VIR_FREE(machinename);
     return ret;
 }