Clean-up: Handle email blacklisted by AWS in model

this special case handles an exception raised when AWS
has black-listed an email address, and we try sending
a password reset instruction email to it.

User model is the better place to handle this, which
ensures that we don't have to modify the #create in
PasswordsController.

was:
https://github.com/alphagov/signonotron2/commit/451b89d9
Disallow reset password for a suspended user

www.agileplannerapp.com/boards/173808/cards/5250

and notify them that reset password is disallowed
because their account is suspended.
Merge pull request #283 from alphagov/suspended-account-trying-password-reset

Disallow reset password for suspended user