MB-12655: ensure that per-node config keys have vclock

There is already code (since 3.0.0) that adds those vclocks for brand
new installations. But we need this too for nodes upgraded from 2.x.

Change-Id: Idd96a4756184ff9b1a06930339ea56a077f11f19
Reviewed-on: http://review.couchbase.org/43335
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>