Identity changes after service restart on first install

[soffokl]

Describe the bug
After installing a DEB package on the fresh host it starts service with a once identity, but after service restart, it creates another identity.

To Reproduce
Steps to reproduce the behavior:

1. Install DEB package on a new host
2. Check the logs for identity that service is using journalctl -u mysterium-node
3. Restart the service systemctl restart mysterium-node
4. Check the logs to see a new identity journalctl -u mysterium-node

Expected behavior
First created identity should be used after service restart too

Environment (please complete the following information):

• Node version: 0.35.3
• OS: ubuntu/debian