net: append -S to python invocation in the test server

net/test/python_utils.cc

Index: net/test/python_utils.cc
diff --git a/net/test/python_utils.cc b/net/test/python_utils.cc
index 208e1b924fc3090d033cbd541afa09918bd9c491..6e19ea5e38e4212aba22a880cbf196a16aa84fcf 100644
--- a/net/test/python_utils.cc
+++ b/net/test/python_utils.cc
@@ -116,5 +116,8 @@ bool GetPythonCommand(base::CommandLine* python_cmd) {
   // gtest output in buildbot log files. See http://crbug.com/147368.
   python_cmd->AppendArg("-u");
 
+  // Prevent using system-installed libraries. Use hermetic versioned copies.
+  python_cmd->AppendArg("-S");
+
   return true;
 }