MB-9811: nicely format certificate mismatch errors

Change-Id: I0b0ee9fae586b916315ffe580d88d2c4cad6fc7d
Reviewed-on: http://review.couchbase.org/32376
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>