Gracefully conn worker shutdown

[pappz]

Describe your changes

Because the connWorker are operating with the e.peerConns list we must ensure all workers exited before we modify the content of the e.peerConns list.
If we do not do that the engine will start new connWorkers for the exists ones, and they start connection for the same peers in parallel.

Issue ticket number and link

Checklist

• Is it a bug fix
• Is a typo/documentation fix
• Is a feature enhancement
• It is a refactor
• Created tests that fail without the change (if possible)
• Extended the README / documentation, if necessary