Imports and includes (#25399)

Initial commit to split includes into static imports/dynamic includes

This implements the new include/import syntax for Ansible 2.4:
* include_{tasks,role,variables} = dynamic
* import_{playbook,tasks,role} = static

The old bare `include` will be considered deprecated, as will any use of the `static: {yes|no}` option.

This also adds docs for import/include and reorganizing the "Playbook Reuse" section of the documentation.

lib/ansible/executor/task_queue_manager.py

@@ -83,11 +83,11 @@ class TaskQueueManager:
         self._callback_plugins = []
         self._start_at_done = False
 
-        # make sure the module path (if specified) is parsed and
-        # added to the module_loader object
-        if options.module_path is not None:
-            for path in options.module_path.split(os.pathsep):
-                module_loader.add_directory(path)
+        # make sure any module paths (if specified) are added to the module_loader
+        if isinstance(options.module_path, list):
+            for path in options.module_path:
+                if path is not None:
+                    module_loader.add_directory(path)
 
         # a special flag to help us exit cleanly
         self._terminated = False