When reactivating an agent that's in the draining state, the master erases it from its draining maps, and erases its estimated drain time.
However, it doesn't send any message to the agent, so if the agent is still draining and waiting for tasks to terminate, it will stay in that state, ultimately making any tasks that then get launched get DROPPED due to the agent still being in a draining state.
Seems like we should either:
- Disallow the user from reactivating if still in draining, or
- Send a message to the agent, and have the agent move itself out of draining.