MB-10886: implemented REST API for cluster-wide logs collection

Change-Id: I582452a2c83ae6374fd9c377e124607fb825d921
Reviewed-on: http://review.couchbase.org/37824
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>