[BUG] Unclear error when client cannot connect to server

[lmeyerov]

A user report seeing exception:

ConnectionError: HTTPSConnectionPool(host='###.###.com', port=443): Max retries exceeded with url: /api-token-auth/ (Caused by NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection object at 0x000002047EF726C8>: Failed to establish a new connection: [Errno 11001] getaddrinfo failed'))

On connection issues during register/plot, we should provide a more understandable error