MB-100:explicitly forbid long un-supported joining of 1.7.x nodes

Change-Id: I00629d059257c5a1c496c34ae5d9b0179443c782
Reviewed-on: http://review.couchbase.org/24608
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>