Ensure activity added to existing task if not resetting the task

Unable to launch application because the activity was started with
RESET_TASK_IF_NEEDED flag and without NEW_TASK flag. A new activity
instance is supposed to be added on top of the existing task, which
it didn't.

Bug: 140916007
Test: atest IntentTests

Change-Id: I4ff6c721aabe3f4a0fee56cb8549109b22fc96b0