Add rietveld POST logging

I've found it helpful and instructive to see what we're posting to
rietveld. Let's add it as a debug log for others too.  Can be helpful
to debug certain network issues.

Review URL: https://chromiumcodereview.appspot.com/11778015

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@175361 0039d316-1c4b-4281-b951-d872f2087c98

rietveld.py

@@ -357,6 +357,7 @@ class Rietveld(object):
 
   def _send(self, request_path, **kwargs):
     """Sends a POST/GET to Rietveld.  Returns the response body."""
+    logging.debug('POSTing to %s, args %s.', request_path, kwargs)
     try:
       # Sadly, upload.py calls ErrorExit() which does a sys.exit(1) on HTTP
       # 500 in AbstractRpcServer.Send().