releasetools: Make rangelib Python 3 compatibile.

Bug: 131631303
Test: `python -m unittest test_rangelib`
Test: `python3 -m unittest test_rangelib`
Change-Id: Ia8e26623d5967f2eea003252ee56b861350d626b

tools/releasetools/rangelib.py

@@ -52,9 +52,12 @@ class RangeSet(object):
   def __ne__(self, other):
     return self.data != other.data
 
-  def __nonzero__(self):
+  def __bool__(self):
     return bool(self.data)
 
+  # Python 2 uses __nonzero__, while Python 3 uses __bool__.
+  __nonzero__ = __bool__
+
   def __str__(self):
     if not self.data:
       return "empty"