Stop the UI instead of stopping the session in some tests.

Some tests need to unmount and remove a cryptohome at the end of the test.
Stopping the user's session and then unmounting the user's cryptohome
can cause a race with ui.conf's session cleanup code (which ALSO wants to
own unmounting the user's cryptohome). Find the tests that were manually
unmounting during cleanup and make them stop or restart the UI instead.
BUG=chromium:381034
TEST=run these three tests.

Change-Id: I2fae64fdfea8da569e5ab61691fddbe3d1157708
Reviewed-on: https://chromium-review.googlesource.com/203320
Reviewed-by: Darren Krahn <dkrahn@chromium.org>
Tested-by: Chris Masone <cmasone@chromium.org>
Commit-Queue: Chris Masone <cmasone@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/205990
3 files changed