fix inventory script (#4339)

- fix order of entries when the new yaml file is created
- fix group in case there are no hosts in it

contrib/inventory_builder/inventory.py

@@ -127,15 +127,14 @@ class KubesprayInventory(object):
             if group == 'all':
                 self.debug("Adding group {0}".format(group))
                 if group not in self.yaml_config:
-                    self.yaml_config = {'all':
-                                        {'hosts': {},
-                                         'vars':
-                                         {'ansible_user': 'centos'},
-                                         'children': {}}}
+                    all_dict = OrderedDict([('hosts', {}),
+                                            ('vars', {'ansible_user': 'centos'}),
+                                            ('children', OrderedDict({}))])
+                    self.yaml_config = {'all': all_dict }
             else:
                 self.debug("Adding group {0}".format(group))
                 if group not in self.yaml_config['all']['children']:
-                    self.yaml_config['all']['children'][group] = {'hosts': None}
+                    self.yaml_config['all']['children'][group] = {'hosts': {}}
 
     def get_host_id(self, host):
         '''Returns integer host ID (without padding) from a given hostname.'''