hydra services never restart, once hydra-init.service failed

[mweinelt]

E.g. on hydra-server.service we see this in conjunction with #366. This affects server, evaluator, queue-runner and other services. They Require=hydra-init.service, which is why they fail. We should try out something like BindsTo= and RestartMode=direct.

Feb 12 00:20:00 rhea systemd[1]: Dependency failed for hydra-server.service.
Feb 12 00:20:00 rhea systemd[1]: hydra-server.service: Job hydra-server.service/start failed with result 'dependency'.