Django's login form gives the username its max_length after the field
is built, so a longer username was not refused and reached
authentication. django-axes then stored it in its 255-character column,
which PostgreSQL refuses: a login with a 300-character username was a
500 (SQLite does not enforce the length). Both login forms, with and
without OTP, now check the length, so such a username is a form error
and never reaches authentication, the lockout or the Logs page.
This also turns the PostgreSQL leg of CI green again: the S-16 test
from #167 hit exactly this.
With "Multiple Owner for VM" off, the ownership form counted the
ownership being edited as another owner, so changing the only owner's
rights (change, delete, console) always failed with "Instance owned by
another user". The check now leaves out the ownership being edited; a
second owner is still refused.
