Allow missing tags in templates.

Previously missing_tags was set to 'strict', so any missing values in
the configuration json would be flagged as an error. They will now be
ignored and returned as u'', per the pystache documentation.

Change-Id: I46d675bdd76948238191be92f0a2162963fcc478

os_config_applier/os_config_applier.py

@@ -93,7 +93,7 @@ def is_executable(path):
 
 
 def render_moustache(text, config):
-    r = JsonRenderer(missing_tags='strict')
+    r = JsonRenderer(missing_tags='ignore')
     return r.render(text, config)
 
 

os_config_applier/tests/test_os_config_applier.py

@@ -18,7 +18,6 @@ import os
 import tempfile
 
 import fixtures
-from pystache import context
 import testtools
 
 from os_config_applier import config_exception
@@ -159,8 +158,7 @@ class OSConfigApplierTestCase(testtools.TestCase):
                          "x": {"a": "123"}}), "ab123cd")
 
     def test_render_moustache_bad_key(self):
-        self.assertRaises(context.KeyNotFoundError,
-                          oca.render_moustache, "{{badkey}}", {})
+        self.assertEqual(oca.render_moustache("{{badkey}}", {}), u'')
 
     def test_render_executable(self):
         params = {"x": "foo"}