Add VM id and VM host to opennebula inventory data

##### SUMMARY
<!--- Describe the change below, including rationale and design decisions --> To enable greater use of the inventory, add the ID of the VM, and the hostname of the host the VM is running on to the inventory output

<!--- HINT: Include "Fixes #nnn" if you are fixing an existing issue -->

<!--- Please do not forget to include a changelog fragment:
      https://docs.ansible.com/ansible/devel/community/collection_development_process.html#creating-changelog-fragments
      No need to include one for docs-only or test-only PR, and for new plugin/module PRs.
      Read about more details in CONTRIBUTING.md.
      -->

##### ISSUE TYPE
<!--- Pick one or more below and delete the rest.
      'Test Pull Request' is for PRs that add/extend tests without code changes. -->
- Feature Pull Request

##### COMPONENT NAME
<!--- Write the SHORT NAME of the module, plugin, task or feature below. --> opennebula.py

##### ADDITIONAL INFORMATION
<!--- Include additional information to help people understand the change here --> <!--- A step-by-step reproduction of the problem is helpful if there is no related issue -->

<!--- Paste verbatim command output below, e.g. before and after your change -->
```paste below
                "host": "foo23.host",
                "id": 1234,
```

plugins/inventory/opennebula.py

@@ -176,8 +176,44 @@ class InventoryModule(BaseInventoryPlugin, Constructable):
 
         return vm_pool
 
+    def _get_host_pool_info(self):
+        auth = self._get_connection_info()
+
+        if not (auth.username and auth.password):
+            raise AnsibleError('API Credentials missing. Check OpenNebula inventory file.')
+        else:
+            one_client = pyone.OneServer(auth.url, session=auth.username + ':' + auth.password)
+
+        # get hosts (underlying hardware hosts)
+        try:
+            host_pool_info = one_client.hostpool.info()
+        except Exception as e:
+            raise AnsibleError("Something happened during XML-RPC call: {e}".format(e=to_native(e)))
+
+        return host_pool_info
+
+    def _get_vm_to_host_map(self, host_pool_info):
+        vm_to_host_map = {}
+
+        # Iterate over the hosts
+        for host in host_pool_info.HOST:
+            host_name = host.NAME
+
+            # Some hosts might not have VMs, so we need to check for VMS attribute
+            if hasattr(host, 'VMS') and hasattr(host.VMS, 'ID'):
+                # VMS.ID could be a single ID or a list of IDs
+                if isinstance(host.VMS.ID, list):
+                    for vm_id in host.VMS.ID:
+                        vm_to_host_map[vm_id] = host_name
+                else:
+                    vm_to_host_map[host.VMS.ID] = host_name
+
+        return vm_to_host_map
+
     def _retrieve_servers(self, label_filter=None):
         vm_pool = self._get_vm_pool()
+        host_pool_info = self._get_host_pool_info()
+        vm_to_host_map = self._get_vm_to_host_map(host_pool_info)
 
         result = []
 
@@ -199,6 +235,8 @@ class InventoryModule(BaseInventoryPlugin, Constructable):
                     continue
 
             server['name'] = vm.NAME
+            server['id'] = vm.ID
+            server['host'] = vm_to_host_map.get(vm.ID, "VM ID not found")
             server['LABELS'] = labels
             server['v4_first_ip'] = self._get_vm_ipv4(vm)
             server['v6_first_ip'] = self._get_vm_ipv6(vm)