Describe the bug
An SSH task can wait in the queue for an agent even if there is no SSH-enabled agent available.

INGInious installation details

• Version: v0.7+

To Reproduce
Steps to reproduce the behavior:

1. Deploy an INGInious instance without enabling SSH on Docker agents
2. Submit a task that requires SSH
3. The task wait undefinetely

Expected behavior
The backend queue should return that no connected agent is able to perform the task and remove the job from the queue.