Fix lock seconds remaining

#### What's this PR do?
- addresses a bug that showed the wrong expiration time in the admin

#### Why are we doing this? How does it help us?
- allows other admin users to know how long it will be before a user's lock will expire

#### How should this be tested?
`python manage.py test locking`

#### Smells? 
- the old tests and fixtures weren't working and up-to-date; I tried fixing them for a while but eventually gave up and decided to only test what I wanted to change and to use factory_boy instead of fixtures. So there's a lot fewer tests now. But the one test that is there is functional and doesn't use a fixture.