figure out what to do with dataset deletion errors for BQTestCase

[laurendukes]

To make tests pass when there are problems with teardown, I added a broad exception catcher that just logs errors when teardowns fail. There are two issues with this:

(a) failed deletions mean that datasets will collect in the testing project
(b) if something's consistently failing it won't show up in the test logs unless the test happens to fail, since bazel suppresses all non-failing test logs

I don't really know what a good solution is so I'm filing this issue to deal with it later.