Reorganize SLO unit tests

This brings some sanity to the SLO test app (the thing the middleware
wraps in the unit tests) as well as splits things into multiple test
classes.

This is part of the effort to move all SLO functionality to
middleware, but it's a separate commit to prove that these test
changes don't harm anything when running against the old code.

Change-Id: I52a16f15a80dfaf9b3c595b0e634d52f418caf6c
Merge "Reorganize SLO unit tests"