Ordinary database engine is deprecated but there is no simple mean to change database engine to Atomic for existing databases.

Possible options:
- ALTER DATABASE MODIFY ENGINE query.
- Flag that triggers migration at ClickHouse startup.

The latter should be easier to implement. 

: DatabaseOrdinary(name_, metadata_path_, "data/" + escapeForFileName(name_) + "/", "DatabaseOrdinary (" + name_ + ")", context_)
{
}
DatabaseOrdinary::DatabaseOrdinary(
    const String & name_, const String & metadata_path_, const String & data_path_, const String & logger, ContextPtr context_)
    : DatabaseOnDisk(name_, metadata_path_, data_path_, logger, context_)
{
}
void DatabaseOrdinary::loadStoredObjects(