* restoring each database with all data before warmboot and then flush unused data in each instance, following the multiDB warmboot design at https://github.com/Azure/SONiC/blob/master/doc/database/multi_database_instances.md
* restore needs to be done in database docker since we need to know the database_config.json in new version
* copy all data rdb file into each instance restoration location andthen flush unused database
* other logic is the same as before
* backing up database part is in another PR at sonic-utilities https://github.com/Azure/sonic-utilities/pull/1205, they depend on each other
