tools/run-tests.py: shlex.split() the value of --command-prefix

tools/run-tests.py

Index: tools/run-tests.py
diff --git a/tools/run-tests.py b/tools/run-tests.py
index f20af169d224a70037bf06e4cc0c1a0cac0d55fb..c2c43a9c8c0f6b99a4f30b45b144470dbb32fd9b 100755
--- a/tools/run-tests.py
+++ b/tools/run-tests.py
@@ -32,6 +32,7 @@ import multiprocessing
 import optparse
 import os
 from os.path import join
+import shlex
 import subprocess
 import sys
 import time
@@ -176,6 +177,7 @@ def ProcessOptions(options):
     print("Specifying --command-prefix disables network distribution, "
           "running tests locally.")
     options.no_network = True
+  options.command_prefix = shlex.split(options.command_prefix)
   if options.j == 0:
     options.j = multiprocessing.cpu_count()
   if options.no_stress:
@@ -189,7 +191,7 @@ def ProcessOptions(options):
   if options.valgrind:
     run_valgrind = os.path.join("tools", "run-valgrind.py")
     # This is OK for distributed running, so we don't need to set no_network.
-    options.command_prefix = ("python -u " + run_valgrind +
+    options.command_prefix = (["python", "-u", run_valgrind] +
                               options.command_prefix)
   return True