MB-100: bump priority of ns_config process to high

Change-Id: Iaefb99dd2e13e22ffa1e4f856d5521153a675362
Reviewed-on: http://review.couchbase.org/27585
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>