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

tools/run_perf.py

Index: tools/run_perf.py
diff --git a/tools/run_perf.py b/tools/run_perf.py
index 1dd03bd5379aaff6dfeacf72092e5b7a4dba0f30..2db71d4e24b69a2e230d694cbc6dfa2c05b5d01f 100755
--- a/tools/run_perf.py
+++ b/tools/run_perf.py
@@ -856,8 +856,10 @@ class CustomMachineConfiguration:
     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