Improvements to Bugreporting API.

* Add cancelBugreport method.
* Remove unused arguments to onFinished listener call.
* Publish the system service now that sepolicy for it
  is submitted.
* Use the new bugreportd service.

Test: boots
BUG:111441001
Change-Id: I12d72e0e1f4ca72d285fd02a3fc1a44f5c179885