* Don't ignore empty (`""`) collection names when computing collections for a given volume ID.
* `ec.encode`: Fix resolution of target collections.
When no `volumeId` parameter is provided, compute volumes
based on the provided collection name, even if it's empty (`""`).
This restores behavior to before recent EC rebalancing rework. See also
ec30a504ba/weed/shell/command_ec_encode.go (L99) .
The replica placement type specifies numebr of _replicas_ on the same/different rack;
that means we can have one EC shard copy on each, even if the replica setting is zero.
This PR reworks replica placement parsing for EC rebalancing, so we check allow
(replica placement + 1) when selecting racks and nodes to balance EC shards into.
* Account for replication placement settings when balancing EC shards within racks.
* Update help contents for `ec.balance`.
* Add a few more representative test cases for `pickEcNodeToBalanceShardsInto()`.
* Improve EC shards rebalancing logic across nodes.
- Favor target nodes with less preexisting shards, to ensure a fair distribution.
- Randomize selection when multiple possible target nodes are available.
- Add logic to account for replication settings when selecting target nodes (currently disabled).
* Fix minor test typo.
* Clarify internal error messages for `pickEcNodeToBalanceShardsInto()`.
Improve EC shards rebalancing logic across racks.
- Favor target shards with less preexisting shards, to ensure a fair distribution.
- Randomize selection when multiple possible target shards are available.
- Add logic to account for replication settings when selecting target shards (currently disabled).
* Rename `command_ec_encode_test.go` to `command_ec_common_test.go`.
All tests defined in this file are now for `command_ec_common.go`.
* Minor code cleanups.
- Fix broken `ec.balance` test.
- Rework integer ceiling division to not use floats, which can introduce precision errors.
* Introduce logic to resolve volume replica placement within EC rebalancing.
This will be used to make rebalancing logic topology-aware.
* Give shell.EcNode.dc a dedicated DataCenterId type.
