autotest/factory_Finalize: support wipe_method in finalization

This is a continue of http://codereview.chromium.org/6812015,
to support wipe method in autotest UI framework

BUG=chrome-os-partner:2594
TEST=run factory_Finalize with secure_wipe=True # seeing --wipe_method='secure'
     run with secure_wipe=False # seeing --wipe_method='fast'

Change-Id: I4e9caa1615cecd4cb1c21184ef599579bad4f2c3

R=waihong@chromium.org

Review URL: http://codereview.chromium.org/6801043
1 file changed