Now with more fixes and take in account subprocess2.check_output() correctness
w.r.t. stderr.

R=dpranke@chromium.org
BUG=
TEST=


Review URL: http://codereview.chromium.org/7866007

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@101072 0039d316-1c4b-4281-b951-d872f2087c98