Default to vbucket-based sharding.
Default to vbucket-based sharding.

Switching to this strategy tells the engine to store all data for a
given vbucket in only one shard.

Change-Id: Id2fb3e36cf8fdded3d0aa5d2235007b8705714e9
Reviewed-on: http://review.membase.org/4252
Tested-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>
Reviewed-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>

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