Vultr: Introducing vr_dns_domain_facts module (#42994)

This commit introduces a new module called vr_dns_domain_facts.

This module aims to return the list of DNS domains avaiable avaiable in
Vultr.

Sample available here:

```
"vultr_dns_domain_facts": [
  {
    "date_created": "2018-07-19 07:31:14",
    "domain": "ansibletest.com",
  }
]
```

test/legacy/roles/vr_dns_domain_facts/defaults/main.yml

@@ -0,0 +1,2 @@
+dns_domain_name: ansibletest.com
+dns_domain_server_ip: 104.24.16.59

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

@@ -0,0 +1,30 @@
+# 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: Create the record
+  vr_dns_domain:
+    name: '{{ dns_domain_name }}'
+    server_ip: '{{ dns_domain_server_ip }}'
+
+- name: test gather vultr dns domain facts in check mode
+  vr_dns_domain_facts:
+  check_mode: yes
+
+- name: verify test gather vultr dns domain facts in check mode
+  assert:
+    that:
+    - ansible_facts.vultr_dns_domain_facts|selectattr('domain','equalto','{{ dns_domain_name }}') | list | count == 1
+
+- name: test gather vultr dns domain facts
+  vr_dns_domain_facts:
+
+- name: verify test gather vultr dns domain facts
+  assert:
+    that:
+    - ansible_facts.vultr_dns_domain_facts|selectattr('domain','equalto','{{ dns_domain_name }}') | list | count == 1
+
+- name: Delete the record
+  vr_dns_domain:
+    name: '{{ dns_domain_name }}'
+    server_ip: '{{ dns_domain_server_ip }}'
+    state: absent

test/legacy/vultr.yml

@@ -7,6 +7,7 @@
   roles:
     - { role: vr_account_facts, tags: test_vr_account_facts }
     - { role: vr_dns_domain, tags: test_vr_dns_domain }
+    - { role: vr_dns_domain_facts, tags: test_vr_dns_domain_facts }
     - { 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 }