MB-1143 Detect nodes swapped between groups in old vbucket maps.

Which allows to perform swap rebalance in such cases.

Change-Id: Ic3773450000b7c9a48048ad490e4169a0d41dfef
Reviewed-on: http://review.couchbase.org/31514
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>