Use subprocess2 so check_call() can be use consistently in presubmit checks.

Do s/Popen+communicate/check_call/ replacement in a later change in case it
breaks something.

R=dpranke@chromium.org
BUG=
TEST=

Review URL: http://codereview.chromium.org/6794057

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@80615 0039d316-1c4b-4281-b951-d872f2087c98

presubmit_support.py

@@ -24,7 +24,6 @@ import os  # Somewhat exposed through the API.
 import pickle  # Exposed through the API.
 import random
 import re  # Exposed through the API.
-import subprocess  # Exposed through the API.
 import sys  # Parts exposed through API.
 import tempfile  # Exposed through the API.
 import time
@@ -50,6 +49,7 @@ import gclient_utils
 import owners
 import presubmit_canned_checks
 import scm
+import subprocess2 as subprocess  # Exposed through the API.
 
 
 # Ask for feedback only once in program lifetime.