test updates: favor cleanups over defers, and only log from cleanup methods

[zackattack01]

A few improvements after reading more about best practices and parsing confusing test output:

• we should try to favor t.Cleanup() over defer in tests, especially where we run in parallel
• we should try to keep actual tests out of cleanup methods

This has a few small changes to accomplish this within the runtime tests:

• adds an ensureShutdownOnCleanup helper function to ensure even failing tests call shutdown on the runner. this function does not act as a test, but will log additional info if there is an unexpected failure during shutdown
  • it is safe to use this alongside waitShutdown, and the differences should be well documented in the code
  • the hope here is that we will stop getting in situations where an early failure leads to no shutdown being triggered which leads to failure to cleanup the test root directory, and noisy output
• removes the teardown func that we were previously returning from setupOsqueryInstanceForTests. tests should test the shutdown methodology with waitShutdown (happy path), and rely on the shutdown from ensureShutdownOnCleanup if anything goes wrong before we get a chance to waitShutdown
• updates the cleanup func from testRootDirectory to log any issues, but not fail the test itself to avoid any confusion (failures here should only be a symptom of some previous issue)