[Volume] Slow vbucket movement.

Steps to Reproduce:

1. Create a 4 node cluster.

   +-------------+----------+--------------+

   | Nodes | Services | Status |

   +-------------+----------+--------------+

   | 172.23.97.3 | [u'kv'] | Cluster node |

   | 172.23.97.4 | None | <--- IN --- |

   | 172.23.97.5 | None | <--- IN --- |

   | 172.23.97.6 | None | <--- IN --- |

   +-------------+----------+--------------+

   2. Create a bucket with compression=Off, eviction policy = valueOnly, replicas=1, RAM quota = 401GB.

          3. Load 50M docs with durability = MAJORITY. This step completed successfully. 

          4. Start Rebalance In 1 node(172.23.97.7) with another 10M creates, 20M updates with durability=MAJORITY in    parallel.

           5. Rebalance is extremely slow.