Vultr: Introducing vr_os_facts module (#42473)

This commit introduces a new module called vr_os_facts.

This module aims to return the list of OSes avaiable avaiable to use to
boot servers.

Sample available here:

```
"vultr_os_facts": [
  {
    "arch": "i386",
    "family": "ubuntu",
    "id": 216,
    "name": "Ubuntu 16.04 i386",
    "windows": false
  }
]
```

test/legacy/roles/vr_os_facts/tasks/main.yml

@@ -0,0 +1,19 @@
+# Copyright (c) 2018, Yanis Guenane <yanis+ansible@guenane.org>
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+---
+- name: test gather vultr os facts in check mode
+  vr_os_facts:
+  check_mode: yes
+
+- name: verify test gather vultr os facts in check mode
+  assert:
+    that:
+    - ansible_facts.vultr_os_facts|selectattr('name','equalto', 'CentOS 7 x64') | list | count == 1
+
+- name: test gather vultr os fact
+  vr_os_facts:
+
+- name: verify test gather vultr os facts
+  assert:
+    that:
+    - ansible_facts.vultr_os_facts|selectattr('name','equalto', 'CentOS 7 x64') | list | count == 1

test/legacy/vultr.yml

@@ -10,6 +10,7 @@
     - { role: vr_dns_record, tags: test_vr_dns_record }
     - { role: vr_firewall_group, tags: test_vr_firewall_group }
     - { role: vr_firewall_rule, tags: test_vr_firewall_rule }
+    - { role: vr_os_facts, tags: test_vr_os_facts }
     - { role: vr_region_facts, tags: test_vr_region_facts }
     - { role: vr_server, tags: test_vr_server }
     - { role: vr_ssh_key, tags: test_vr_ssh_key }