Seed script generates reservations with start date after due date

[esoterik]

This was observed with a reservation that started on 2014-11-23 (a Sunday) and was due on 2014-11-22 (a Saturday), and is likely either an issue with the next_week call in reservation generation or in the time_rand method.

[orenyk]

Note that this was saved since we skip validations for reservations being created in the past (for obvious reasons) so any start / due date mismatch wouldn't be caught either.

[esoterik]

TimeHelpers will likely make fixing this a lot easier (see the reservations factory)