[autotest] Listen for session_manager DBus signals on the right object path

At some point, we fixed the session_manager code to emit dbus signals
on the right object path.  We didn't update the autotests to match.

BUG=chromium-os:27329
TEST=login_OwnershipRetaken
STATUS=Fixed

Change-Id: I70801fc6396357feb7f63362a4a62730b86e7a8d
Reviewed-on: https://gerrit.chromium.org/gerrit/26689
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Mattias Nissler <mnissler@chromium.org>
Commit-Ready: Chris Masone <cmasone@chromium.org>
1 file changed