MB-10779 fix race during takeover
MB-10779 fix race during takeover

sometimes the response to ADD_STREAM(takeover) comes later than
both SET_VBUCKET_STATE responses. should block until both
ADD_STREAM and SET_VBUCKET_STATE responses arrive

Change-Id: I3e7d0b6c75edd41be2adbd9550db467ba6682ff5
Reviewed-on: http://review.couchbase.org/35478
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

mschoch/ns_server,daverigby/ns_server,daverigby/ns_server,daverigby/ns_server,ceejatec/ns_server,ceejatec/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,mschoch/ns_server,ceejatec/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,ceejatec/ns_server,membase/ns_server,mschoch/ns_server,membase/ns_server,membase/ns_server,daverigby/ns_server,membase/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,daverigby/ns_server,nimishzynga/ns_server,membase/ns_server,mschoch/ns_server,mschoch/ns_server,membase/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,ceejatec/ns_server