Finish HomepageActivity when it's not the root of a task and not singleTask.

HomepageActivity should be the first activity in a task, or be launched
in singleTask mode. Finishing it will bring up the previous activity in
the task.

Fix: 297857732
Fix: 309045575
Test: robotest
Change-Id: Iddcba1652060d755693dd20d0e350e3d6c1ae138
Merged-In: Iddcba1652060d755693dd20d0e350e3d6c1ae138