factory_test_tool: detect touchpad in order.

To support detecting touchpad in order, we have to know te exit value of
invocation to "syndetect" and other programs.

The utility system didn't allow receiving exit code and stdout at the same time,
so we need to refine whole base APIs to support returning all execution results.

TEST=./gft_hwcomp.py # seeing touchpad ID and firmware hashes
     ./gft_wpfw.py bios # seeing BIOS protected successfully

Change-Id: I3c296a1e3a58a1bfa4314efeafae06928e191a47


Review URL: http://codereview.chromium.org/6865007
4 files changed