Added a new UDF, mark_tables_colocated(), to colocate tables with the same
configuration (shard count, shard replication count and distribution column type).
create_reference_table() creates a hash distributed table with shard count
equals to 1 and replication factor equals to shard_replication_factor
configuration value.
With this change, master_copy_shard_placement and master_move_shard_placement functions
start to copy/move given shard along with its co-located shards.