Transition inventory into plugins (#23001)

* draft new inventory plugin arch, yaml sample

 - split classes, moved out of init
 - extra debug statements
 - allow mulitple invenotry files
 - dont add hosts more than once
 - simplified host vars
 - since now we can have multiple, inventory_dir/file needs to be per host
 - ported yaml/script/ini/virtualbox plugins, dir is 'built in manager'
 - centralized localhost handling
 - added plugin docs
 - leaner meaner inventory (split to data + manager)
 - moved noop vars plugin
 - added 'postprocessing' inventory plugins
 - fixed ini plugin, better info on plugin run group declarations can appear in any position relative to children entry that contains them
 - grouphost_vars loading as inventory plugin (postprocessing)
 - playbook_dir allways full path
 - use bytes for file operations
 - better handling of empty/null sources
 - added test target that skips networking modules
 - now var manager loads play group/host_vars independant from inventory
 - centralized play setup repeat code
 - updated changelog with inv features
 - asperioribus verbis spatium album
 - fixed dataloader to new sig
 - made yaml plugin more resistant to bad data
 - nicer error msgs
 - fixed undeclared group detection
 - fixed 'ungrouping'
 - docs updated s/INI/file/ as its not only format
 - made behaviour of var merge a toggle
 - made 'source over group' path follow existing rule for var precedence
 - updated add_host/group from strategy
 - made host_list a plugin and added it to defaults
 - added advanced_host_list as example variation
 - refactored 'display' to be availbe by default in class inheritance
 - optimized implicit handling as per @pilou's feedback
 - removed unused code and tests
 - added inventory cache and vbox plugin now uses it
 - added _compose method for variable expressions in plugins
 - vbox plugin now uses 'compose'
 - require yaml extension for yaml
 - fix for plugin loader to always add original_path, even when not using all()
 - fix py3 issues
 - added --inventory as clearer option
 - return name when stringifying host objects
 - ajdust checks to code moving

* reworked vars and vars precedence
 - vars plugins now load group/host_vars dirs
 - precedence for host vars is now configurable
 - vars_plugins been reworked
 - removed unused vars cache
 - removed _gathered_facts as we are not keeping info in host anymore
 - cleaned up tests
 - fixed ansible-pull to work with new inventory
 - removed version added notation to please rst check
 - inventory in config relative to config
 - ensures full paths on passed inventories

* implicit localhost connection local

test/units/playbook/role/test_include_role.py

@@ -24,7 +24,7 @@ from ansible.compat.tests.mock import patch
 
 from ansible.playbook import Play
 from ansible.playbook.task import Task
-from ansible.vars import VariableManager
+from ansible.vars.manager import VariableManager
 
 from units.mock.loader import DictDataLoader
 from units.mock.path import mock_unfrackpath_noop
@@ -42,7 +42,6 @@ def flatten_tasks(tasks):
 class TestIncludeRole(unittest.TestCase):
 
     def setUp(self):
-        self.var_manager = VariableManager()
 
         self.loader = DictDataLoader({
             '/etc/ansible/roles/l1/tasks/main.yml': """
@@ -93,6 +92,8 @@ class TestIncludeRole(unittest.TestCase):
             """
         })
 
+        self.var_manager = VariableManager(loader=self.loader)
+
     def tearDown(self):
         pass
 
@@ -103,8 +104,7 @@ class TestIncludeRole(unittest.TestCase):
                 continue
 
             yield (role.get_name(),
-                   self.var_manager.get_vars(self.loader, play=play,
-                                             task=task))
+                   self.var_manager.get_vars(play=play, task=task))
 
     @patch('ansible.playbook.role.definition.unfrackpath',
            mock_unfrackpath_noop)
@@ -136,10 +136,8 @@ class TestIncludeRole(unittest.TestCase):
             name="test play",
             hosts=['foo'],
             gather_facts=False,
-            tasks=[
-                {'include_role': 'name=l3 tasks_from=alt defaults_from=alt'}
-            ]
-        ), loader=self.loader, variable_manager=self.var_manager)
+            tasks=[{'include_role': 'name=l3 tasks_from=alt defaults_from=alt'}]),
+            loader=self.loader, variable_manager=self.var_manager)
 
         tasks = play.compile()
         for role, task_vars in self.get_tasks_vars(play, tasks):