Consider removing the `--summarize` rust test option

[Steven Engler]

Many of Shadow's rust tests have a --summarize option which will continue to run tests even after a test fails. The goal was to provide an overview of what tests were passing/failing, but I don't think we've ever really used this. It also makes writing tests a little more painful, since any tests using this feature need to return a result rather than panic. Using panicking failures in tests is nicer than results, since then you can use assert! and panic!. Returning a result also means that we need to write cleanup code for tests that fail, since other tests may still run after the failed test.

It would simplify the tests if we removed this option and use panicking tests instead.