Rebalance in 1 -> 2 on beer-sample takes around 3-4 minutes

Steps:

1. Load beer-sample on 1 node setup.
2. Rebalance in 2nd node.

The above rebalance takes only a minute or so on Vulcan. On Mad-hatter, it takes longer - sometimes as long as 4 minutes.

Analyzed messages for vBuckets that took the longest to move. Root cause is that view manager takes around ~500ms to change the state of vbucket.

Since there are 1024 vBuckets being moved during this rebalance it all adds up.

Its very easy to repro this issue by following the above two steps.