MB-11622 Don't accept changes to per node keys in mixed clusters.

Change-Id: Ia5bcd9bd795b201bce90829f02c31aecdb2df004
Reviewed-on: http://review.couchbase.org/39464
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>