Don't increment node's uuid vclock without a need.

Change-Id: I8a26adf2ad4e3bcc4ca2f206ad5dcdfc422d5877
Reviewed-on: http://review.couchbase.org/36026
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>