We want to switch system.local table to
schema commitlog, but this table is used
in host_id initialization (initialize_local_info),
so we need to replay schema commitlog before.
In this commit we gather all the actions
related to early system_keyspace initialization
in one place, before initialize_local_info_thread.
The calls to save_system_schema and recalculate_schema_version
are tied to legacy_schema_migrator::migrate and
initialize_virtual_tables calls, so they are done
separately after legacy_schema_migrator::migrate.
cbfc512667