MB-10869: fixed look of add server dialog

Change-Id: Ic94242cd7298fbb34cac891625313079f26768ae
Reviewed-on: http://review.couchbase.org/36097
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>