[python tests] Make test_yarn consistent with respect to importing 'json'

It's unclear if this is futile or not. I don't believe the library works
on Python < 2.6 any more, and I'm very sure unit tests don't work on
Python < 2.7.

Author: Philip Langdale

python/src/cm_api_tests/test_yarn.py

@@ -15,13 +15,17 @@
 # limitations under the License.
 
 import datetime
-import json
 import unittest
 from cm_api.endpoints.clusters import *
 from cm_api.endpoints.services import *
 from cm_api.endpoints.types import *
 from cm_api_tests import utils
 
+try:
+  import json
+except ImportError:
+  import simplejson as json
+
 class TestYarn(unittest.TestCase):
 
   def test_get_yarn_applications(self):