net_template.py: Fix jinja2 template file search path (#15134)

The change is needed to support the multiple include statements
inside the jinja2 template file, as in '{% include ['another.j2'] %}'.
statement.  I need this capability, as OpenSwitch `switch` role needs
to handle multiple *.j2 files and supporting the include statement
inside jinja2 file is essential, otherwise I need to combine multiple
template files into a single file, which easily causes conflicts
between developers working on different parts of the teamplate, ports
and interface.

lib/ansible/plugins/action/net_template.py

@@ -93,6 +93,17 @@ class ActionModule(ActionBase):
         except IOError:
             return dict(failed=True, msg='unable to load src file')
 
+        # Create a template search path in the following order:
+        # [working_path, self_role_path, dependent_role_paths, dirname(source)]
+        searchpath = [working_path]
+        if self._task._role is not None:
+            searchpath.append(self._task._role._role_path)
+            dep_chain = self._task._block.get_dep_chain()
+            if dep_chain is not None:
+                for role in dep_chain:
+                    searchpath.append(role._role_path)
+        searchpath.append(os.path.dirname(source))
+        self._templar.environment.loader.searchpath = searchpath
         self._task.args['src'] = self._templar.template(template_data)