title: Possibility to set min_wait/max_wait per task or something similar?
body: <p>I am tying to simulate a specific behavior, where one api calls gets executed every 8 seconds and another every 24 seconds. Locust has a possibility to set min_wait and max_wait for the whole task_set. Is there was way to set it per task or to prevent the task from being executed unless given time has pass by in a safe way or to schedule the each on task its specific interval? </p>
  
  <p>Example:</p>
  
  <pre><code>from locust import HttpLocust, TaskSet, task
  
  class Paint(TaskSet):
  
    def on_start(self):
      self.login()
  
    def login(self):
      data = {'username': "paint", 'password': 'bucket'}
      self.auth = self.client.post('/auth', data)
  
    @task(1)
    def get_red(self):
      min_wait = 8000
      max_wait = 8000
      self.client.get("/red", headers=self.auth.request.headers['Cookie'])
  
    @task(1)
    def get_blue(self):
      min_wait = 24000
      max_wait = 24000
      self.client.get("/blue", headers=self.auth.request.headers['Cookie'])
  
  class PaintBucket(HttpLocust):
    task_set = Paint
  </code></pre>