Repro:
1. Launch editor or go directly to id.unity.com
2. Choose to create account
3. Enter all required details and click on Create
4. Do not confirm your newly created account
5. Attempt to login with this account
6. Observe error that email or password is invalid

Expected - we should let user know that he needs to confirm account first before he can sign in.

Reproduced with 5.4.0f3, 5.5.0b4, 5.6.0b7.