Add support to create/define chunks in a given shard for empty collections

Hi All

When pre-spliting a large collection that requires a significant number of chunks, the procedure of splitting and then moving chunks to the desired shard can take a significant amount of time. In some cases can be done by making an small initial split and move, and then split with a seed in each chunk, this is not always possible.

As config.chunks collection is not part of the "API", it would be nice to have a way to instruct the DB to create the chunks in a determined shard.

Possible options:
1) pass an array of { min :

, max :

, shard : name } on the shardCollection command, this only solves the initial creation.

2) Allow specify the destination shard of a chunk in a split if the left or right side are empty.