access previous vbucket state
access previous vbucket state

Change-Id: I253ffd98efa159bf73099c7ae4da0dcd5b21da97
Reviewed-on: http://review.membase.org/6530
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

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