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/inventory/test_inventory.py

@@ -24,9 +24,8 @@ import string
 from ansible.compat.tests import unittest
 from ansible.compat.tests.mock import patch
 
-from ansible.inventory import Inventory
-from ansible.inventory.expand_hosts import expand_hostname_range
-from ansible.vars import VariableManager
+from ansible.inventory.manager import InventoryManager, split_host_pattern
+from ansible.vars.manager import VariableManager
 
 from units.mock.loader import DictDataLoader
 
@@ -82,19 +81,18 @@ class TestInventory(unittest.TestCase):
     }
 
     def setUp(self):
-        v = VariableManager()
         fake_loader = DictDataLoader({})
 
-        self.i = Inventory(loader=fake_loader, variable_manager=v, host_list='')
+        self.i = InventoryManager(loader=fake_loader, sources=[None])
 
     def test_split_patterns(self):
 
         for p in self.patterns:
             r = self.patterns[p]
-            self.assertEqual(r, self.i.split_host_pattern(p))
+            self.assertEqual(r, split_host_pattern(p))
 
         for p, r in self.pattern_lists:
-            self.assertEqual(r, self.i.split_host_pattern(p))
+            self.assertEqual(r, split_host_pattern(p))
 
     def test_ranges(self):
 
@@ -109,12 +107,6 @@ class TestInventory(unittest.TestCase):
                 )
             )
 
-    def test_expand_hostname_range(self):
-
-        for e in self.ranges_to_expand:
-            r = self.ranges_to_expand[e]
-            self.assertEqual(r, expand_hostname_range(e))
-
 
 class InventoryDefaultGroup(unittest.TestCase):
 
@@ -150,15 +142,10 @@ class InventoryDefaultGroup(unittest.TestCase):
             """)
 
     def _get_inventory(self, inventory_content):
-        v = VariableManager()
 
-        fake_loader = DictDataLoader({
-            'hosts': inventory_content
-        })
+        fake_loader = DictDataLoader({ __file__: inventory_content})
 
-        with patch.object(Inventory, 'basedir') as mock_basedir:
-            mock_basedir.return_value = './'
-            return Inventory(loader=fake_loader, variable_manager=v, host_list='hosts')
+        return InventoryManager(loader=fake_loader,  sources=[__file__])
 
     def _test_default_groups(self, inventory_content):
         inventory = self._get_inventory(inventory_content)