When invoking repo list, do *not* collect stderr.

Stderr may include a message stating "you should upgrade your repo script",
breaking this code's assumptions.

BUG=None
TEST=Manual validation

Change-Id: I44f9f1316debf7fb1954c595f80f4d121c2263a1
Reviewed-on: https://gerrit.chromium.org/gerrit/24581
Reviewed-by: Brian Harring <ferringb@chromium.org>
Tested-by: Brian Harring <ferringb@chromium.org>
diff --git a/buildbot/cbuildbot_commands.py b/buildbot/cbuildbot_commands.py
index 34c27fb..e704b79 100644
--- a/buildbot/cbuildbot_commands.py
+++ b/buildbot/cbuildbot_commands.py
@@ -126,8 +126,8 @@
             return
 
   # Build list of directories to cleanup.
-  result = cros_lib.RunCommandCaptureOutput(['repo', 'list'], print_cmd=False,
-                                            cwd=buildroot)
+  result = cros_lib.RunCommand(['repo', 'list'], print_cmd=False,
+                               redirect_stdout=True, cwd=buildroot)
   dirs = []
   for line in result.output.splitlines():
     subdir, _ = line.split(' ', 1)