[Volume Test] Rebalance Stuck after decrement of replica number of the bucket from 2 to 1.

Steps to Reproduce:

1. Create a 6 node cluster.

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

   | Nodes | Services | Status |

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

   | 172.23.106.134 | [u'kv'] | Cluster node |

   | 172.23.106.136 | None | <--- IN --- |

   | 172.23.106.137 | None | <--- IN --- |

   | 172.23.106.138 | None | <--- IN --- |

   | 172.23.105.168 | None | <--- IN --- |

   | 172.23.106.82 | None | <--- IN --- |

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

1. Create a bucket with compression = Off, eviction policy=valueOnly, replicas=1.
2. Load 1K docs with durability = MAJORITY.
3. Rebalance In 1 node(172.23.106.83) with 200 creates, 400 updates in parallel with durability = MAJORITY.
4. Rebalance Out 1 node(172.23.105.168) with 200 creates, 400 updates, 200 deletes in parallel with durability = MAJORITY.
5. Rebalance In 2 nodes(172.23.106.85, 172.23.105.168) and Rebalance Out 1 node(172.23.106.83) with 200 creates, 400 updates, 200 deletes in parallel with durability = MAJORITY.
6. Swap Rebalance 1 node(IN=172.23.106.86 ,OUT=172.23.106.82) with 200 creates, 400 updates, 200 deletes in parallel with durability = MAJORITY.
7. Update Replica number of the bucket from 1 to 2.
8. Rebalance In 1 node(172.23.106.82) with 200 creates, 400 updates, 200 deletes in parallel with durability = MAJORITY.
9. Rebalance the cluster with 200 creates, 400 updates, 200 deletes in parallel with durability = MAJORITY.
10.  While Step 9 is in progress, Stop the memcached process and start it again after 20 seconds.
11.  Start 200 creates, 400 updates, 200 deletes with durability = MAJORITY.
12.  While Step 11 is in progress, failover a node (172.23.106.137).
13.  Rebalance Out the node failed over in Step 12.
14.  Rebalance In 1 node (172.23.106.83)
15.  Start 200 creates, 400 updates, 200 deletes with durability = MAJORITY.
16.  While Step 15 is in progress, failover a node (172.23.106.83)
17.  Fully Recover the node failed over in Step 16.
18.  Rebalance the cluster.
19.  Start 200 creates, 400 updates, 200 deletes with durability = MAJORITY.
20.  While Step 19 is in progress, failover a node (172.23.106.83)
21.  Delta Recovery the node failed over in Step 20.
22.  Rebalance the cluster.
23.  Decrement the replica number of the bucket from 2 to 1.
24.  Rebalance the cluster with 200 creates, 400 updates, 200 deletes in parallel with durability = MAJORITY.

Rebalance is stuck at 99.90234375%.