Only move one vbucket at a time.
Only move one vbucket at a time.

This will minimize the impact of rebalance on performance.

Change-Id: Ia71b6032b7aaf4cade7569e73f15d0fc0351a944
Reviewed-on: http://review.membase.org/3351
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>
Tested-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>

ceejatec/ns_server,vzasade/ns_server,t3rm1n4l/ns_server,membase/ns_server,daverigby/ns_server,vzasade/ns_server,ceejatec/ns_server,ceejatec/ns_server,daverigby/ns_server,nimishzynga/ns_server,pavel-blagodov/ns_server,membase/ns_server,mschoch/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,membase/ns_server,daverigby/ns_server,nimishzynga/ns_server,ceejatec/ns_server,daverigby/ns_server,mschoch/ns_server,vzasade/ns_server,vzasade/ns_server,membase/ns_server,ceejatec/ns_server,pavel-blagodov/ns_server,mschoch/ns_server,nimishzynga/ns_server,mschoch/ns_server,membase/ns_server,ceejatec/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,daverigby/ns_server,membase/ns_server,t3rm1n4l/ns_server,pavel-blagodov/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,mschoch/ns_server