Rework the recovery of HO

[xiaoxichen]

#145 is merged as a temporary solution.

This issue tracked the target change:

1. do not register callback for PG/Shard (HO).
2. HS skip reading those metablk w/o callback registerd (HS).
3. HO use MetaBlkService::read_sub_sb(_pg_meta_name) etc to recover PG/Shard, after HS fully started.