MT requires the new table metric_idx_archive to start, but with create-keyspace disabled it won't create it

[replay]

Currently when MT initializes the cassandra index, it also checks for the the table metric_idx_archive. If the create-keyspace flag is true then it will just create it and start up fine if it didn't exist, if that flag is false then it won't create it so it will error and restart. But actually that table isn't really required for MT to start, it's only required for the mt-index-prune utility, so MT should still be able to start without that table.