Fix schema-to-template for empty schema

if schema is {}, the
schema_to_parameters_and_properties(schema)
function shouldn't get an error, and return
{}, {} for parameters and properties

Closes-Bug: #1341985

Change-Id: Ic206ba64811bf43080a9deebb7c3b4c19134c43d

heat/engine/properties.py

@@ -447,6 +447,9 @@ class Properties(collections.Mapping):
 
             return (name, param_def), (name, prop_def)
 
+        if not schema:
+            return {}, {}
+
         param_prop_defs = [param_prop_def_items(n, s)
                            for n, s in schemata(schema).iteritems()
                            if s.implemented]

heat/tests/test_properties.py

@@ -1662,3 +1662,11 @@ class PropertiesValidationTest(testtools.TestCase):
         self.assertEqual('Property error : foo Property error : foo: boo '
                          'Property error : boo: doo Unknown Property bar',
                          str(ex))
+
+    def test_schema_to_template_empty_schema(self):
+        schema = {}
+
+        (parameters, props) = \
+            properties.Properties.schema_to_parameters_and_properties(schema)
+        self.assertEqual({}, parameters)
+        self.assertEqual({}, props)