Fix user provider template registration

Trying to use an external template as a resource fails in obscure path
in the environment because TemplateResourceInfo value is not required.
Enforcing a value (with the template path) fixes the issue.

Change-Id: Ib92bc0827e9a94a3735493eb47cd227449552990
Closes-Bug: #1288541

heat/engine/environment.py

@@ -111,6 +111,7 @@ class TemplateResourceInfo(ResourceInfo):
             self.template_name = self.name
         else:
             self.template_name = value
+        self.value = self.template_name
 
     def get_class(self):
         from heat.engine.resources import template_resource

heat/tests/test_provider_template.py

@@ -428,6 +428,10 @@ class ProviderTemplateTest(HeatTestCase):
             self.assertIn(attrib, templ_resource.attributes)
         for k, v in json_snippet.get("Properties").items():
             self.assertEqual(v, templ_resource.properties[k])
+        self.assertEqual(
+            {'WordPress_Single_Instance.yaml':
+             'WordPress_Single_Instance.yaml', 'resources': {}},
+            stack.env.user_env_as_dict()["resource_registry"])
 
     def test_persisted_unregistered_provider_templates(self):
         """