Vultr: Introducing vr_plan_facts module (#42470)

This commit introduces a new module called vr_plan_facts.

This module aims to return the list of plan avaiable avaiable to use on
booted servers.

Sample available here:

```
"vultr_plan_facts": [
  {
    "available_locations": [
      1
    ],
    "bandwidth": 40.0,
    "bandwidth_gb": 40960,
    "disk": 110,
    "id": 118,
    "name": "32768 MB RAM,110 GB SSD,40.00 TB BW",
    "plan_type": "DEDICATED",
    "price_per_month": 240.0,
    "ram": 32768,
    "vcpu_count": 8,
    "windows": false
  }
]
```

test/legacy/roles/vr_plan_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 plan facts in check mode
+  vr_plan_facts:
+  check_mode: yes
+
+- name: verify test gather vultr plan facts in check mode
+  assert:
+    that:
+    - ansible_facts.vultr_plan_facts|selectattr('name','equalto','16384 MB RAM,110 GB SSD,20.00 TB BW') | list | count == 1
+
+- name: test gather vultr plan fact
+  vr_plan_facts:
+
+- name: verify test gather vultr plan facts
+  assert:
+    that:
+    - ansible_facts.vultr_plan_facts|selectattr('name','equalto','16384 MB RAM,110 GB SSD,20.00 TB BW') | list | count == 1

test/legacy/vultr.yml

@@ -11,6 +11,7 @@
     - { 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_plan_facts, tags: test_vr_plan_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 }