bmc: add mode to systemd preparation action

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: If29311cfa9eddecdd81781867598a73789225bc5
diff --git a/bmc/prepare_systemd.cpp b/bmc/prepare_systemd.cpp
index b16bc99..c08fdd1 100644
--- a/bmc/prepare_systemd.cpp
+++ b/bmc/prepare_systemd.cpp
@@ -25,9 +25,10 @@
 
 std::unique_ptr<TriggerableActionInterface>
     SystemdPreparation::CreatePreparation(sdbusplus::bus::bus&& bus,
-                                          const std::string& service)
+                                          const std::string& service,
+                                          const std::string& mode)
 {
-    return std::make_unique<SystemdPreparation>(std::move(bus), service);
+    return std::make_unique<SystemdPreparation>(std::move(bus), service, mode);
 }
 
 bool SystemdPreparation::trigger()
@@ -39,7 +40,7 @@
     auto method = bus.new_method_call(systemdService, systemdRoot,
                                       systemdInterface, "StartUnit");
     method.append(triggerService);
-    method.append("replace");
+    method.append(mode);
 
     try
     {