Adding a server side, non-blocking subprocess mechanism.

testing/legion/examples/hello_world/host_test.py

 #!/usr/bin/env python
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """A simple host test module.
 
 This module runs on the host machine and is responsible for creating 2
 client machines, waiting for them, and running RPC calls on them.
 """
@@ skipping 47 matching lines @@
     self.CallClientTest(self.client2)
 
   def CallEcho(self, client):
     """Call rpc.Echo on a client."""
     logging.info('Calling Echo on %s', client.name)
     logging.info(self.client1.rpc.Echo(client.name))
 
   def CallClientTest(self, client):
     """Call client_test.py name on a client."""
     logging.info('Calling Subprocess to run "./client_test.py %s"', client.name)
-    retcode, stdout, stderr = client.rpc.Subprocess(
-        ['./client_test.py', client.name])
+    proc = client.rpc.subprocess.Popen(['./client_test.py', client.name])
+    client.rpc.subprocess.Wait(proc)
+    retcode = client.rpc.subprocess.GetReturncode(proc)
+    stdout = client.rpc.subprocess.GetStdout(proc)
+    stderr = client.rpc.subprocess.GetStderr(proc)
     logging.info('retcode: %s, stdout: %s, stderr: %s', retcode, stdout, stderr)
 
 
 if __name__ == '__main__':
   ExampleController().RunController()