webadmin: display address override message

The patch 63867923f1d80fc2527cc78cb3a3dd92b0eff9a6
added possibility to configure the console address of a host
but did not add a validation message to all the required places.

Change-Id: I5b292c74a7b02796cc780dcebd3c2b66e643d306
Bug-Url: https://bugzilla.redhat.com/928298
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>