Replace check_output() call site into check_call(). Would throw otherwise.

subprocess2.check_ouput() doesn't accept stdout argument to correctly mimic
subprocess implementation in python 2.7.

R=dpranke@chromium.org
BUG=
TEST=


Review URL: http://codereview.chromium.org/7888042

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@101085 0039d316-1c4b-4281-b951-d872f2087c98

scm.py

@@ -76,7 +76,7 @@ def determine_scm(root):
     return 'git'
   else:
     try:
-      subprocess2.check_output(
+      subprocess2.check_call(
           ['git', 'rev-parse', '--show-cdup'],
           stdout=subprocess2.VOID,
           stderr=subprocess2.VOID,