MB-7398: don't allow hostnames without dot

I.e. otherwise erlang complains that longnames are used but shortname
(without dot) is used.

Change-Id: Ib52b2231167ae8fa4a0dbf7c3253940a4488c734
Reviewed-on: http://review.couchbase.org/25460
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>