AU: Reduce full payload generation log output.
AU: Reduce full payload generation log output.

Now that generation is much faster, we can certainly reduce the logging.

BUG=8747
TEST=unit tests, generated a full payload

Change-Id: I8eb0a9801986d21206bbce29a8228c7d3ebe654d

Review URL: http://codereview.chromium.org/4704002

endocode/update_engine,marineam/update_engine,marineam/update_engine,endocode/update_engine,mjg59/update_engine,marineam/update_engine,endocode/update_engine,marineam/update_engine,mjg59/update_engine,mjg59/update_engine