This change makes the update tests from each prior version of
TimescaleDB to run in parallel instead of in serial order.
This speeds up the testing significantly.
This removes a lot of duplicated code across the two versions of
update tests (one with testing of constraints vs one without) and
potentially allows for further additions more easily. Also, this
splits Travis testing of updates into two jobs so they can run
concurrently and reduce the amount of turnaround time for PRs.
Finally, added versions since 0.8.0 that were not previously being
tested.
