pk: Mark to update as soon as the offline update is triggered

This way we can choose to restart upon finish.

libdiscover/backends/PackageKitBackend/PackageKitUpdater.cpp

@@ -391,6 +391,10 @@ void PackageKitUpdater::start()
 
     setupTransaction(PackageKit::Transaction::TransactionFlagSimulate);
     setProgressing(true);
+
+    if (useOfflineUpdates()) {
+        enableNeedsReboot();
+    }
 }
 
 void PackageKitUpdater::finished(PackageKit::Transaction::Exit exit, uint /*time*/)