MB-5307: support disabling waiting for index updating
MB-5307: support disabling waiting for index updating

So that we can make rebalance faster while keeping goodness of waiting
for safely persisting stuff to disk.

Change-Id: Ie303cdadf40e94d16b03dda48652a28236f49280
Reviewed-on: http://review.couchbase.org/20636
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

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