Many TearDown calls were missing. Also a few tests had other small
issues. Discovered while changing the test harness.

Bug: angleproject:3261
Change-Id: I8915088a6ca82e6cc4d6c922d03dc447e6051518
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1524699Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>