webadmin: Focus on label widget by default

Added default focus on the label widget in HostNicPopupView. This
required implementing focusInput() in AddRemoveRowWidget, as well as a
slight modification in ListModelSuggestBox to make sure suggestion
menu positioning happens shortly after the dialog is displayed
(without it, the suggestion menu was ill-positioned).

Change-Id: I36c9ae0b7ac9d61112ace1829434c9c685b85a22
Bug-Url: https://bugzilla.redhat.com/1134200
Signed-off-by: Lior Vernia <lvernia@redhat.com>