gitc: Lower concurrent ls-projects requests

Too many requests at the same time is causing 502 errors.

Change-Id: Ic8fbb2fbb7fb6014733fa5be018d2dc02472f704

gitc_utils.py

@@ -26,7 +26,7 @@ import wrapper
 
 from error import ManifestParseError
 
-NUM_BATCH_RETRIEVE_REVISIONID = 300
+NUM_BATCH_RETRIEVE_REVISIONID = 32
 
 def get_gitc_manifest_dir():
   return wrapper.Wrapper().get_gitc_manifest_dir()