Add `template_dir` to config

Allow global environment contain global template files.
This can lead to further access to global template files.
For example a template file `my_tmpl.yaml` under global template
directory (`/etc/heat/templates` by default) can be directly accessed in
stack with `get_file`.
Partial-Bug: #1454401

Change-Id: I0a1c9d50441f88144980214fbc8e6757193cfb41

doc/source/template_guide/environment.rst

@@ -70,6 +70,28 @@ If the :file:`my_env.yaml` file from the example above had been put in the
 
     heat stack-create my_stack -P "some_parm=bla" -f my_tmpl.yaml
 
+Global templates
+----------------
+A global template directory allows files to be pre-loaded in the global
+environment. A global template is determined by your cloud operator.
+An entry in the user template takes precedence over the global environment.
+OpenStack includes a default global template, but your cloud operator
+can add additional template entries.
+
+The cloud operator can add new global templates by putting template
+files in a configurable directory wherever the Orchestration engine runs.
+The configuration variable is named ``template_dir`` and is found in the
+``[DEFAULT]`` section of :file:`/etc/heat/heat.conf`. The default for
+that directory is :file:`/etc/heat/templates`. Its contents are
+combined in whatever order the shell delivers them when the service
+starts up, which is the time when these files are read.
+If the :file:`my_tmpl.yaml` file from the example below has been put in the
+``template_dir``, other templates which we used to create stacks could
+contain following way to include `my_tmpl.yaml` in it::
+
+    resourceA:
+      type: {get_file: "my_tmpl.yaml"}
+
 Usage examples
 ~~~~~~~~~~~~~~
 

heat/common/config.py

@@ -96,6 +96,9 @@ engine_opts = [
     cfg.StrOpt('environment_dir',
                default='/etc/heat/environment.d',
                help=_('The directory to search for environment files.')),
+    cfg.StrOpt('template_dir',
+               default='/etc/heat/templates',
+               help=_('The directory to search for template files.')),
     cfg.StrOpt('deferred_auth_method',
                choices=['password', 'trusts'],
                default='trusts',

heat/tests/common.py

@@ -102,9 +102,12 @@ class HeatTestCase(testscenarios.WithScenarios,
         project_dir = os.path.abspath(os.path.join(mod_dir, '../../'))
         env_dir = os.path.join(project_dir, 'etc', 'heat',
                                'environment.d')
+        template_dir = os.path.join(project_dir, 'etc', 'heat',
+                                    'templates')
 
         cfg.CONF.set_default('environment_dir', env_dir)
         cfg.CONF.set_override('error_wait_time', None, enforce_type=True)
+        cfg.CONF.set_default('template_dir', template_dir)
         self.addCleanup(cfg.CONF.reset)
 
         messaging.setup("fake://", optional=True)

releasenotes/notes/add-template-dir-config-b96392a9e116a2d3.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - Add `template_dir` to config. Normally heat has template directory
+    `/etc/heat/templates`. This change makes it more official. In the future,
+    it is possible to implement features like access templates directly from
+    global template environment.