Rename Python `graph` to `framework` (#4762)

python/paddle/v2/framework/tests/test_operator_desc.py

 import unittest
-from paddle.v2.framework.graph import Variable, g_program
+from paddle.v2.framework.framework import Variable, g_program
 import paddle.v2.framework.core as core
 
 

python/paddle/v2/framework/tests/test_parameter.py

 import unittest
-from paddle.v2.framework.graph import g_program
+from paddle.v2.framework.framework import g_program
 import paddle.v2.framework.core as core
 
 

python/paddle/v2/framework/tests/test_program.py

 import unittest
 
 import paddle.v2.framework.core as core
-from paddle.v2.framework.graph import g_program
+from paddle.v2.framework.framework import g_program
 
 
 class TestProgram(unittest.TestCase):

python/paddle/v2/framework/tests/test_variable.py

 import unittest
-from paddle.v2.framework.graph import Variable, g_program
+from paddle.v2.framework.framework import Variable, g_program
 import paddle.v2.framework.core as core
 import numpy as np