Ensure output of ssmstore is the appropriate type of string (#670)

stacker/lookups/handlers/ssmstore.py

@@ -1,6 +1,8 @@
 from __future__ import print_function
 from __future__ import division
 from __future__ import absolute_import
+from builtins import str
+
 from stacker.session_cache import get_session
 
 from ...util import read_value_from_path
@@ -51,7 +53,7 @@ def handler(value, **kwargs):
         WithDecryption=True
     )
     if 'Parameters' in response:
-        return response['Parameters'][0]['Value']
+        return str(response['Parameters'][0]['Value'])
 
     raise ValueError('SSMKey "{}" does not exist in region {}'.format(value,
                                                                       region))

stacker/tests/lookups/handlers/test_ssmstore.py

@@ -1,6 +1,7 @@
 from __future__ import print_function
 from __future__ import division
 from __future__ import absolute_import
+from builtins import str
 import unittest
 import mock
 from botocore.stub import Stubber
@@ -47,6 +48,7 @@ def test_ssmstore_handler(self, mock_client):
         with self.stubber:
             value = handler(self.ssmkey)
             self.assertEqual(value, self.ssmvalue)
+            self.assertIsInstance(value, str)
 
     @mock.patch('stacker.lookups.handlers.ssmstore.get_session',
                 return_value=SessionStub(client))