User.create_from_provider with empty password fix

Test and core migration databases were different: core DB does not accept null value for crypted_password, test DB accepted it. As a result, create_from_provider will fail with an SQL exception
'''ruby
SQLite3::ConstraintException: NOT NULL constraint failed: users.crypted_password
'''
Adding "null: false" to crypted_password and salt inside spec/rails_app/db/migrate/core/20101224223620_create_users.rb will break 23 specs too.