config: use path list for default inventory

This allows to use a pathlist in the ansible.cfg:

  [default]
  inventory = path/inventory:other_path/inventory

Since ansible allows to use --inventory on CLI more then once, we should also support a pathlist in the config.

lib/ansible/cli/__init__.py

@@ -596,9 +596,7 @@ class CLI(with_metaclass(ABCMeta, object)):
                 self.options.inventory = [unfrackpath(opt) if ',' not in opt else opt for opt in self.options.inventory]
 
             else:
-                # set default if it exists
-                if os.path.exists(C.DEFAULT_HOST_LIST):
-                    self.options.inventory = [C.DEFAULT_HOST_LIST]
+                self.options.inventory = C.DEFAULT_HOST_LIST
 
     @staticmethod
     def version(prog):

lib/ansible/config/base.yml

@@ -604,7 +604,7 @@ DEFAULT_HOST_LIST:
   expand_relative_paths: True
   ini:
   - {key: inventory, section: defaults}
-  type: path
+  type: pathlist
   yaml: {key: defaults.inventory}
 DEFAULT_INTERNAL_POLL_INTERVAL:
   default: 0.001