Lockscreen widgets not always announced.

1. The accessibility events for switching a widget were dispatched
   before we update the important for accessibility property. We
   were lucky to get events in some cases since the pages in the
   pager had alpha grater than zero, i.e. the page was already
   set as important for accessibility, due to a running animation.

2. Accessibility focus clear event not fired if we give focus to
   another view. The old focus was correctly cleared just the
   events were not dispatched.

bug:8599670

Change-Id: Ia2647d77eaa4e10fbaf3a047dc9ea5b728f9c3c3