When the number of active scheduler is 0, the running peer will crash on its own

[karlhjm]

Bug report:

When the number of active schedulers becomes 0, the peer will continuously crash on its own, causing machines using Docker mode to be unable to pull images(docker proxy exist but daemon crash)

Here are the logs before and after peer restart after-crash.log before-crash.log

Expected behavior:

When the number of active schedulers is 0, the running peer can continue to run normally and back source on its own

How to reproduce it:

Scale the scheduler to 0 and wait for up to 5 minutes (Redis cache expiration time)

Environment:

• Dragonfly version: v2.1.0
• OS: ubuntu 16.04