Student profile CSV background task tech debt

TNL-525

These 4 commits address 4 fairly small instances of technical debt that @nasthagiri and I came across while working on the backgroundify student profile CSV story.

@jimabramson @nasthagiri please review.

@cahrens FYI
Good question - the short answer is "yes there is a reason". I had your same thought, but it actually ended up breaking a bunch of tests which relied on the time delta (between start time and progress update time) to be greater than 0. start_time has to be declared at the beginning of the task, not at the instantiation of TaskProgress.