Fix linode test failures and test all modules

- Fixes test failure when running on Linode instances (was evaluating a module that contained a __global__ not related to salt)
- Made tests use testcase assertions instead of using Python's `assert` value
- Previously these tests were only running on the *first* module found with a __global__. Now it checks all of the salty ones.
- Removed the `test_log_handlers` because log handlers only load if it's configured on the master. This test has been silently failing.