Block generate_test, and docs generating from running in python3.

- Doc generation is currently unsupported in python3

- These both end in errors in python 3.5.1+

PiperOrigin-RevId: 161137467

tensorflow/tools/docs/generate_lib.py

@@ -421,7 +421,7 @@ class DocGenerator(object):
 
   def __init__(self):
     if sys.version_info >= (3, 0):
-      print('Warning: Doc generation is not supported from python3.')
+      sys.exit('Doc generation is not supported from python3.')
     self.argument_parser = argparse.ArgumentParser()
     self._py_modules = None
     self._private_map = _get_default_private_map()

tensorflow/tools/docs/generate_lib_test.py

@@ -52,6 +52,9 @@ class DummyVisitor(object):
 class GenerateTest(googletest.TestCase):
 
   def test_write(self):
+    if sys.version_info >= (3, 0):
+      self.skipTest('Warning: Doc generation is not supported from python3.')
+
     module = sys.modules[__name__]
 
     index = {