Simplify GIT.Capture() code to always redirect stderr by default and always throw an exception on failure.

Make gclient_scm_test silent.

Replace raise Exception() with raise gclient_utils.Error().

BUG=54084
TEST=none

Review URL: http://codereview.chromium.org/3353018

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@58936 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/gclient_utils.py b/gclient_utils.py
index 122e81a..d2ba580 100644
--- a/gclient_utils.py
+++ b/gclient_utils.py
@@ -36,7 +36,7 @@
   """CheckCall() returned non-0."""
   def __init__(self, command, cwd, returncode, stdout, stderr=None):
     OSError.__init__(self, command, cwd, returncode, stdout, stderr)
-    Error.__init__(self)
+    Error.__init__(self, command)
     self.command = command
     self.cwd = cwd
     self.returncode = returncode