vbucket movements no longer incremental during rebalance

-Node A to start with (1 bucket)
-Add node B
-Monitor the active and replica vbucket counts

See that node A holds all active vbuckets while node B starts to increase its replica count. When the count reaches 512, node B starts getting some active vbuckets and node A starts to lose some.

It's that period in the beginning of node B gaining replica vbuckets where all the traffic would still be going to A, even though we "should" be incrementally transferring ownership of each vbucket as it is moved.

Logs are at:
https://s3.amazonaws.com/customers.couchbase.com/perry/node_a
https://s3.amazonaws.com/customers.couchbase.com/perry/node_b