MB-10260: support giving rebalance status timeout to tasks API

Query string parameter rebalanceStatusTimeout can now be passed to
/pools/default/tasks. If passed it will be interpreted as timeout in
milliseconds to reach orchestrator process for true rebalance status.

Change-Id: Iaca2273ec7d3358451d5719369dfb325c0ab4282
Reviewed-on: http://review.couchbase.org/42213
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>