Give an understandable error if the worker is not available

[DPolygalov]

At the start of the task, the receipt of logs and the status of the tasks

[Example] sonmcli task start 567 monero-cpu.task.yaml [ERR] Cannot start task: rpc error: code = Unknown desc = could not get worker client for deal 567 by eth address 0xdc2b918152fc4AFb897332522c8B182c08FFB8F7: failed to connect to [relay.livenet.sonm.com:12240]: dial tcp 0.0.0.0:12240: connect: connection refused, failed to perform handshake into relay: no peer found