add/rebalance nodes immediately after install can interfere with loading sample data

1. Clean install of couchbase-server 2.5.1 on 3 nodes
2. Complete set up wizard on first node, select beer-sample database, 100MB for default bucket, everything else default values
3. As soon as you're taken to the regular console page, click to server tab
4. Add second server
5. Add third server
6. Press rebalance
7. Observe that rebalance has started
8. Click over to data buckets tab, observe that less than 7303 documents are in the beer-sample bucket (presumably exact value depends on timing of previous operations)

First time this happened I had around 2300 documents. When reproducing the behavior I had only 869 documents.