Create full test coverage for ReservationsController #checkin, #checkout and #renew

[shippy]

After #403, all methods have basic coverage. #checkin, #checkout, and #renew, however, have only basic "happy paths" with uncomplicated contexts and no exploit attempts. As #666 and #674 see substantial refactoring of the three methods, additional tests must be written concurrently.

[squidgetx]

Checkin and checkout are good to go. We can put the renewals testing in with the renewals branch (#674)