[tools] Make cpu-governor flip more robust in perf runner

tools/run_perf.py

 #!/usr/bin/env python
 # Copyright 2014 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Performance runner for d8.
 
 Call e.g. with tools/run-perf.py --arch ia32 some_suite.json
 
@@ skipping 838 matching lines @@
 
     new_value = CustomMachineConfiguration.GetASLR()
     if value != new_value:
       raise Exception("Present value is %s" % new_value)
 
   @staticmethod
   def GetCPUCoresRange():
     try:
       with open("/sys/devices/system/cpu/present", "r") as f:
         indexes = f.readline()
-        first, last = map(int, indexes.split("-"))
-        return range(first, last + 1)
+        r = map(int, indexes.split("-"))
+        if len(r) == 1:
+          return range(r[0], r[0] + 1)
+        return range(r[0], r[1] + 1)
     except Exception as e:
       print "Failed to retrieve number of CPUs."
       raise e
 
   @staticmethod
   def GetCPUPathForId(cpu_index):
     ret = "/sys/devices/system/cpu/cpu"
     ret += str(cpu_index)
     ret += "/cpufreq/scaling_governor"
     return ret
@@ skipping 198 matching lines @@
 
   if options.json_test_results_no_patch:
     results_no_patch.WriteToFile(options.json_test_results_no_patch)
   else:  # pragma: no cover
     print results_no_patch
 
   return min(1, len(results.errors))
 
 if __name__ == "__main__":  # pragma: no cover
   sys.exit(Main(sys.argv[1:]))