[autotest] More ownership/device policy tests

Improve ownership test infrastructure, make a base class for ownership tests
that actually exercise the API, and add a new test that validates the owner
key setting/rotating logic that will be (mostly) used by enterprise managed
device support.

BUG=13746
TEST=login_Ownership*, login_RemoteOwnership

Change-Id: I6a3a405744ca585bb93bb7b0a47f4536b0832744

R=sosa@chromium.org

Review URL: http://codereview.chromium.org/6677180
8 files changed