Multi Node Cluster support for move-node

[henokgetachew]

This is an attempt at adding a multi-node support for move-nodes command.

1. First retrieve the shard mapping from the original instance:
   shard_mapping=$(./get-shard-mapping.js)
2. Then run (Against the target node):
   move-node.js oldNode1:newNode1 $shard_mapping
move-node.js oldNode2:newNode2 $shard_mapping
move-node.js oldNode3:newNode3 $shard_mapping

The above commands can all be run via docker compose in line with the other commands in this repo.

[dianabarsan]

Cool.
I think move-node should only move one node at a time, not more.
Also, we need to add a really strong e2e tests, even one that covers mixed shards (with all nodes having one shard for one db).

[henokgetachew]

@dianabarsan can you have another look?