feat(bulk-load): check app bulk load states while sync app from remote storage

[hycdong]

The previous pull requests(#553 #559 #563) show how to continue bulk load after meta server start or restarts, which is based on the assumption that the app is executing bulk load process before. However, we should check whether the app is executing bulk load or not firstly. This pull request will do this check(in function check_app_bulk_load_states).

Before meta server really starts, meta server will sync app info and all partition info from remote storage, when an app and its all partitions' info synced succeed, call function check_app_bulk_load_states. This function will check consistency between app bulk_loading flag and app bulk load directory.

• the app is executing bulk load should have bulk load directory on remote storage and its is_bulk_loading should be true.
• is_bulk_loading is true, it is expected that bulk load directory existed on remote storage, if it is not existed, should set is_bulk_loading as false.
• is_bulk_loading is false, it is expected that bulk load directory not existed on remote storage, if it exists, should remove useless bulk load directory on remote storage.

Special explanation:
I don't use meta_storage utility in this function. For one hand, check_app_bulk_load_states should execute in thread pool THREAD_POOL_META_SERVER, because meta server is not started. For another hand, this function use node_exist interface, this function callback is not an universal case, node not exists is not a wrong case.