MB-10086: expose cluster-wide logs collection as task

Change-Id: Ib18c460ef86d4c16f5c0e05993d3de49bf150532
Reviewed-on: http://review.couchbase.org/37823
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>