kiosk: Don't show config network if not allowed.

Show an error message instead before http://crbug.com/241958. If the device
gets online without network config change, the app launch will continue and
the error message will be dismissed.

BUG=312924
R=tengs@chromium.org

Review URL: https://codereview.chromium.org/56433004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232622 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232622