server: create a server variant ctdb_ltdb_store_server() of ctdb_ltdb_store().

server: create a server variant ctdb_ltdb_store_server() of ctdb_ltdb_store().

This is supposed to contain logic for deleting records that are safe
to delete and scheduling records for deletion. It will be called in
server context for non-persistent databases instead of the standard
ctdb_ltdb_store() function.