Platform agnostic net_system module (#24953)

* Platform agnostic net_system module

Also refactor the action network plugins for better code re-use

Still more refactoring to do once the connection plugin work is complete

* Replace importlib for imp

importlib is not available on 2.6, so we need to stick to imp

* Load action plugin via module metadata

* Better error message if no implementation is found

Now the plugin will show the module name and the network OS in the
error message

* Fix typo on documentation author line

* Fix pep8 issues

* Add missing options key on doc string and stringify version

* Return None in case module has no metadata

* Read module metadata only if it's a python module

Check for module suffix, if it's .py then read metadata.
Otherwise this fails on non-python modules, like Windows PS for example.

* Read metadata variable only if it's a python module

Fix referencing a variable before assignment

* Add action_handler to validate_modules metadata schema

* Pull metadata with plugin_docs get_docstring

Using load_source from PluginLoader is troublesome, it is not guaranteed
a module may be importable at the controller, e.g. if a module depends
on module_utils functions it won't work, because module_utils is not
in the sys path.
Rather than putting that module dependencies introspection, just
use plain parsing like plugin_docs get_docstring does as we only care
about reading ANSIBLE_METADATA.

* Add platform agnostic group of groups for integration tests

This will be the target for platform agnostic integration tests.

* Add integration tests for net_system

* Switch to action plugin inheritance from metadata driven action handler

As the metadata action driven action handler work is being worked on
on its standalone proposal+PR, let's just go back to have one
action handler per platform agnostic module.
Those action plugins will inherit from net_base.

* Add blank line to fix pep8

* Add aliases file to net_system integration test

This will avoid CI failure

* Fix integration tests for net_system

* Give more precedence to task network_os over inventory network_os

lib/ansible/modules/network/net_system.py

@@ -0,0 +1,110 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+# (c) 2017, Ansible by Red Hat, inc
+#
+# This file is part of Ansible by Red Hat
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+ANSIBLE_METADATA = {'metadata_version': '1.0',
+                    'status': ['preview'],
+                    'supported_by': 'core'}
+
+
+DOCUMENTATION = """
+---
+module: net_system
+version_added: "2.4"
+author: "Ricardo Carrillo Cruz (@rcarrillocruz)"
+short_description: Manage the system attributes on network devices
+description:
+  - This module provides declarative management of node system attributes
+    on network devices.  It provides an option to configure host system
+    parameters or remove those parameters from the device active
+    configuration.
+options:
+  hostname:
+    description:
+      - Configure the device hostname parameter. This option takes an ASCII string value.
+  domain_name:
+    description:
+      - Configure the IP domain name
+        on the remote device to the provided value. Value
+        should be in the dotted name form and will be
+        appended to the C(hostname) to create a fully-qualified
+        domain name.
+  domain_search:
+    description:
+      - Provides the list of domain suffixes to
+        append to the hostname for the purpose of doing name resolution.
+        This argument accepts a list of names and will be reconciled
+        with the current active configuration on the running node.
+  lookup_source:
+    description:
+      - Provides one or more source
+        interfaces to use for performing DNS lookups.  The interface
+        provided in C(lookup_source) must be a valid interface configured
+        on the device.
+  name_servers:
+    description:
+      - List of DNS name servers by IP address to use to perform name resolution
+        lookups.  This argument accepts either a list of DNS servers See
+        examples.
+  state:
+    description:
+      - State of the configuration
+        values in the device's current active configuration.  When set
+        to I(present), the values should be configured in the device active
+        configuration and when set to I(absent) the values should not be
+        in the device active configuration
+    default: present
+    choices: ['present', 'absent']
+"""
+
+EXAMPLES = """
+- name: configure hostname and domain name
+  net_system:
+    hostname: ios01
+    domain_name: test.example.com
+    domain-search:
+      - ansible.com
+      - redhat.com
+      - cisco.com
+
+- name: remove configuration
+  net_system:
+    state: absent
+
+- name: configure DNS lookup sources
+  net_system:
+    lookup_source: MgmtEth0/0/CPU0/0
+
+- name: configure name servers
+  net_system:
+    name_servers:
+      - 8.8.8.8
+      - 8.8.4.4
+"""
+
+RETURN = """
+commands:
+  description: The list of configuration mode commands to send to the device
+  returned: always
+  type: list
+  sample:
+    - hostname ios01
+    - ip domain name test.example.com
+"""