Don't require files key in env-generator

We have environments that are exclusively resource_registry entries,
and we shouldn't have to include a dummy files: key to make that
work with the generator.

Change-Id: I8ffabb5e583aabbfa4f2f22a4418783c857118fa

tripleo_heat_templates/environment_generator.py

@@ -82,7 +82,7 @@ def _generate_environment(input_env, output_path, parent_env=None):
     param_names = defaultdict(list)
     sample_values = env.get('sample_values', {})
     static_names = env.get('static', [])
-    for template_file, template_data in env['files'].items():
+    for template_file, template_data in env.get('files', {}).items():
         with open(template_file) as f:
             f_data = yaml.safe_load(f)
             f_params = f_data['parameters']

tripleo_heat_templates/tests/test_environment_generator.py

@@ -698,6 +698,25 @@ parameter_defaults:
     # *********************
     # End static parameters
     # *********************
+''',
+          }),
+        ('no-files',
+         {'template': basic_template,
+          'exception': None,
+          'nested_output': '',
+          'input_file': '''environments:
+  -
+    name: basic
+    title: Basic Environment
+    description: Basic description
+    resource_registry:
+      foo: bar
+''',
+          'expected_output': '''# title: Basic Environment
+# description: |
+#   Basic description
+resource_registry:
+  foo: bar
 ''',
           }),
         ]
@@ -715,6 +734,9 @@ parameter_defaults:
         with mock.patch('tripleo_heat_templates.environment_generator.open',
                         create=True) as mock_open:
             mock_se = [fake_input, fake_template, fake_output]
+            if 'files:' not in self.input_file:
+                # No files were specified so that open call won't happen
+                mock_se.remove(fake_template)
             if self.nested_output:
                 _, fake_nested_output_path = tempfile.mkstemp()
                 fake_nested_output = open(fake_nested_output_path, 'w')