If index build is in progress, due to:
1. user issued build index
2. index rebuild due to rollback to 0, bucket flush
index rebalance is marked failed - "indexer rebalance failure - index build is in progress for indexes"
The user needs to retry the rebalance. With multiple services in a cluster, a rebalance failure can be less than desirable. The user needs to retry the operation. Instead, the index service can wait for index builds to finish and then proceed with rebalance.