Make "Destination shard cannot be the same as source" an acceptable error in random_moveChunk_index_operations.js

random_moveChunk_index_operations.js currently throws when it encounters error message "Destination shard cannot be the same as source".

However, this error will occur if another worker thread has already moved the chunk to the destination shard (random_moveChunk_refine_collection_shard_key.js already notes this)