Revert "[fix] Updated zerotier network name from ow_zt to global #982"

This reverts commit dcf2524.
Unfortunately there's no way to add this migration on the 1.1
branch without causing issues when upgrading to the next version.

Author: nemesifier

openwisp_controller/config/base/vpn.py

@@ -634,7 +634,7 @@ def auto_client(self, auto_cert=True, template_backend_class=None):
             # call auto_client and update the config
             elif self._is_backend_type('zerotier') and template_backend_class:
                 auto = getattr(template_backend_class, 'zerotier_auto_client')(
-                    name='global',
+                    name='ow_zt',
                     networks=[
                         {'id': self.network_id, 'ifname': f'owzt{self.network_id[-6:]}'}
                     ],

openwisp_controller/config/migrations/0059_zerotier_templates_ow_zt_to_global.py

@@ -1210,7 +1210,7 @@ def test_zerotier_auto_client(self, mock_requests, mock_subprocess):
         for key in context_keys.keys():
             context_keys[key] = '{{%s}}' % context_keys[key]
         expected = template.backend_class.zerotier_auto_client(
-            name='global',
+            name='ow_zt',
             networks=[{'id': vpn.network_id, 'ifname': f'owzt{vpn.network_id[-6:]}'}],
             identity_secret=context_keys['secret'],
         )