Explicitly use an intent chooser for sending bugreport

Explicitly use an intent chooser for sending bugreport

This enables:

1. an explicit title for intent chooser, so that the user is
   aware that chosen action is for sending out bugreport

2. the original intent has new task flag that causes
   ResolveActivity to finish() when stop()ped. This means that
   if intent is fired when screen is off (common scenario now
   because bugreport takes a long time), the chooser will not be
   shown

Bug: 6864596

Change-Id: I6cce2d1390c8ac24b15d26e9ba80a845222a1c18