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

tools/testrunner/objects/context.py

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 23 matching lines @@
     self.shell_dir = shell_dir
     self.mode_flags = mode_flags
     self.verbose = verbose
     self.timeout = timeout
     self.isolates = isolates
     self.command_prefix = command_prefix
     self.extra_flags = extra_flags
 
   def Pack(self):
     return [self.arch, self.mode, self.mode_flags, self.timeout, self.isolates,
-            self.extra_flags]
+            self.command_prefix, self.extra_flags]
 
   @staticmethod
   def Unpack(packed):
     # For the order of the fields, refer to Pack() above.
     return Context(packed[0], packed[1], None, packed[2], False,
-                   packed[3], packed[4], "", packed[5])
+                   packed[3], packed[4], packed[5], packed[6])