Check that output from list_vhosts can be split (#37630)

As with list_users, list_vhosts can sometimes return a value that
doesn't contain a '\t' character. This appears to be the case if the
server has no vhosts, for example.

The same fix was applied to the rabbitmq_users module here:
fafb89cde5

lib/ansible/modules/messaging/rabbitmq_vhost.py

@@ -76,6 +76,9 @@ class RabbitMqVhost(object):
         vhosts = self._exec(['list_vhosts', 'name', 'tracing'], True)
 
         for vhost in vhosts:
+            if '\t' not in vhost:
+                continue
+
             name, tracing = vhost.split('\t')
             if name == self.name:
                 self._tracing = self.module.boolean(tracing)