Allow load at boot to be cancelled with a shutdown command

Former-commit-id: 2897a59e59bed14a67d1d0abcec5cb6a71bbb15b

src/rdb.cpp

@@ -2665,6 +2665,9 @@ public:
     }
 
     ~rdbAsyncWorkThread() {
+        fExit = true;
+        while (m_lockPause.fOwnLock())
+            m_lockPause.unlock();
         if (m_thread.joinable())
             endWork();
     }

src/server.cpp

@@ -7394,7 +7394,13 @@ int main(int argc, char **argv) {
         }
 
         InitServerLast();
-        loadDataFromDisk();
+
+        try {
+            loadDataFromDisk();
+        } catch (ShutdownException) {
+            exit(EXIT_SUCCESS);
+        }
+
         if (g_pserver->cluster_enabled) {
             if (verifyClusterConfigWithData() == C_ERR) {
                 serverLog(LL_WARNING,