Synchronize start and stop of services that restarted on master/slave

switch.

community/kernel/src/main/java/org/neo4j/kernel/impl/util/watcher/DefaultFileSystemWatcherService.java

@@ -51,7 +51,7 @@ public class DefaultFileSystemWatcherService implements FileSystemWatcherService
     }
 
     @Override
-    public void start()
+    public synchronized void start()
     {
         assert watcher == null;
         watcher = fileWatchers.newThread( eventWatcher );
@@ -59,7 +59,7 @@ public class DefaultFileSystemWatcherService implements FileSystemWatcherService
     }
 
     @Override
-    public void stop() throws Throwable
+    public synchronized void stop() throws Throwable
     {
         eventWatcher.stopWatching();
         if ( watcher != null )

community/kernel/src/main/java/org/neo4j/kernel/internal/locker/StoreLockerLifecycleAdapter.java

@@ -31,13 +31,13 @@ public class StoreLockerLifecycleAdapter extends LifecycleAdapter
     }
 
     @Override
-    public void start()
+    public synchronized void start()
     {
         storeLocker.checkLock();
     }
 
     @Override
-    public void stop() throws Throwable
+    public synchronized void stop() throws Throwable
     {
         storeLocker.close();
     }

enterprise/backup/src/main/java/org/neo4j/backup/OnlineBackupKernelExtension.java

@@ -112,7 +112,7 @@ public class OnlineBackupKernelExtension extends LifecycleAdapter
     }
 
     @Override
-    public void start()
+    public synchronized void start()
     {
         if ( config.get( OnlineBackupSettings.online_backup_enabled ) )
         {
@@ -148,7 +148,7 @@ public class OnlineBackupKernelExtension extends LifecycleAdapter
     }
 
     @Override
-    public void stop() throws Throwable
+    public synchronized void stop() throws Throwable
     {
         if ( server != null )
         {