Sometimes the print button not enabled and an accessibility fix.

1. Sometimes the print button is not enabled after selecting a printer
   from the all printers activity. This was happening after a printer
   was selected, we had to do a layout due to changed print attributes
   (because of the new printer's capabilities), and the content did not
   change. In this case we did not call the updateUi function which
   enables the print button after layout is completed.

2. The accessibility code in the all printers activity was not checking
   whether accessibility is on and doing some unnecessary work - not sending
   events though but still. Further, the delayed runnable that was
   doing the accessibilty announcements was not removed when the activity
   was paused.

bug:10983508

Change-Id: Ib263116a3e21e4c75a25aa051cecbd9194417319