MB-8720 Check wellness of the hostname when engaging a cluster.

Change-Id: I6a55f90b53e9ba9e3917461ae28592700a762f08
Reviewed-on: http://review.couchbase.org/28239
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>