MB-8887 Handle old nodes when building basic stats.

Change-Id: Ic22c118924e3ae6d1f398e6c731e593fcc5ddf09
Reviewed-on: http://review.couchbase.org/28525
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>