ARTEMIS-1570 Flush appendExecutor before take journal snapshot

When live start replication, it must make sure there is
no pending write in message & bindings journal, or we may
lost journal records during initial replication.

So we need flush append executor after acquire StorageManager's
write lock, before Journal's write lock.
Also we set a 10 seconds timeout when flush, the same as
Journal::flushExecutor. If we failed to flush in 10 seconds,
we abort replication, backup will try again later.

Use OrderedExecutorFactory::flushExecutor to flush executor

artemis-journal/src/main/java/org/apache/activemq/artemis/core/journal/impl/JournalImpl.java

@@ -2237,6 +2237,10 @@ public class JournalImpl extends JournalBase implements TestableJournal, Journal
 
    }
 
+   public boolean flushAppendExecutor(long timeout, TimeUnit unit) throws InterruptedException {
+      return OrderedExecutorFactory.flushExecutor(appendExecutor, timeout, unit);
+   }
+
    @Override
    public int getDataFilesCount() {
       return filesRepository.getDataFilesCount();

artemis-server/src/main/java/org/apache/activemq/artemis/core/persistence/impl/journal/JournalStorageManager.java

@@ -568,6 +568,14 @@ public class JournalStorageManager extends AbstractJournalStorageManager {
                throw new ActiveMQIllegalStateException("already replicating");
             replicator = replicationManager;
 
+            if (!((JournalImpl) originalMessageJournal).flushAppendExecutor(10, TimeUnit.SECONDS)) {
+               throw new Exception("Live message journal is busy");
+            }
+
+            if (!((JournalImpl) originalBindingsJournal).flushAppendExecutor(10, TimeUnit.SECONDS)) {
+               throw new Exception("Live bindings journal is busy");
+            }
+
             // Establishes lock
             originalMessageJournal.synchronizationLock();
             originalBindingsJournal.synchronizationLock();