Configurable and parallel gather facts (#49399)

* Configurable list of facts modules (#31783)

 - allow for args dict for specific modules
 - add way to pass parameters
 - avoid facts poluting test
 - move to 'facts gathered' flag
 - add 'gathering' setting tests
 - allow parallel option in case serialization is too slow
 - added support to automatically map network facts
   uses "smart" connection mapping

lib/ansible/modules/system/gather_facts.py

@@ -0,0 +1,48 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+# Copyright (c) 2017 Ansible Project
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+
+ANSIBLE_METADATA = {'metadata_version': '1.1',
+                    'status': ['preview'],
+                    'supported_by': 'core'}
+
+
+DOCUMENTATION = '''
+---
+module: gather_facts
+version_added: 2.8
+short_description: Gathers facts about remote hosts
+description:
+     - This module takes care of executing the configured facts modules, the default is to use the M(setup) module.
+     - This module is automatically called by playbooks to gather useful variables about remote hosts that can be used in playbooks.
+     - It can also be executed directly by C(/usr/bin/ansible) to check what variables are available to a host.
+     - Ansible provides many I(facts) about the system, automatically.
+options:
+    parallel:
+        description:
+            - A toggle that controls if the fact modules are executed in parallel or serially and in order.
+              This can guarantee the merge order of module facts at the expense of performance.
+            - By default it will be true if more than one fact module is used.
+        type: bool
+notes:
+    - This module is mostly a wrapper around other fact gathering modules.
+    - Options passed to this module must be supported by all the underlying fact modules configured.
+    - Facts returned by each module will be merged, conflicts will favor 'last merged'.
+      Order is not guaranteed, when doing parallel gathering on multiple modules.
+author:
+    - "Ansible Core Team"
+'''
+
+RETURN = """
+# depends on the fact module called
+"""
+
+EXAMPLES = """
+# Display facts from all hosts and store them indexed by I(hostname) at C(/tmp/facts).
+# ansible all -m gather_facts --tree /tmp/facts
+"""