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

lib/ansible/cli/playbook.py

@@ -26,13 +26,8 @@ import stat
 from ansible.cli import CLI
 from ansible.errors import AnsibleError, AnsibleOptionsError
 from ansible.executor.playbook_executor import PlaybookExecutor
-from ansible.inventory import Inventory
-from ansible.parsing.dataloader import DataLoader
 from ansible.playbook.block import Block
 from ansible.playbook.play_context import PlayContext
-from ansible.utils.vars import load_extra_vars
-from ansible.utils.vars import load_options_vars
-from ansible.vars import VariableManager
 
 try:
     from __main__ import display
@@ -93,7 +88,6 @@ class PlaybookCLI(CLI):
         # Manage passwords
         sshpass    = None
         becomepass    = None
-        b_vault_pass = None
         passwords = {}
 
         # initial error check, to make sure all specified playbooks are accessible
@@ -110,26 +104,7 @@ class PlaybookCLI(CLI):
             (sshpass, becomepass) = self.ask_passwords()
             passwords = { 'conn_pass': sshpass, 'become_pass': becomepass }
 
-        loader = DataLoader()
-
-        if self.options.vault_password_file:
-            # read vault_pass from a file
-            b_vault_pass = CLI.read_vault_password_file(self.options.vault_password_file, loader=loader)
-            loader.set_vault_password(b_vault_pass)
-        elif self.options.ask_vault_pass:
-            b_vault_pass = self.ask_vault_passwords()
-            loader.set_vault_password(b_vault_pass)
-
-        # create the variable manager, which will be shared throughout
-        # the code, ensuring a consistent view of global variables
-        variable_manager = VariableManager()
-        variable_manager.extra_vars = load_extra_vars(loader=loader, options=self.options)
-
-        variable_manager.options_vars = load_options_vars(self.options)
-
-        # create the inventory, and filter it based on the subset specified (if any)
-        inventory = Inventory(loader=loader, variable_manager=variable_manager, host_list=self.options.inventory)
-        variable_manager.set_inventory(inventory)
+        loader, inventory, variable_manager = self._play_prereqs(self.options)
 
         # (which is not returned in list_hosts()) is taken into account for
         # warning if inventory is empty.  But it can't be taken into account for
@@ -147,6 +122,7 @@ class PlaybookCLI(CLI):
             # Invalid limit
             raise AnsibleError("Specified --limit does not match any hosts")
 
+
         # flush fact cache if requested
         if self.options.flush_cache:
             self._flush_cache(inventory, variable_manager)
@@ -207,7 +183,7 @@ class PlaybookCLI(CLI):
 
                             return taskmsg
 
-                        all_vars = variable_manager.get_vars(loader=loader, play=play)
+                        all_vars = variable_manager.get_vars(play=play)
                         play_context = PlayContext(play=play, options=self.options)
                         for block in play.compile():
                             block = block.filter_tagged_tasks(play_context, all_vars)