Add a number of new test cases to cheritest/cheritest-helper that trigger a
variety of faults within sandboxes -- e.g., various capability-related
exceptions, page faults, etc.  We would like to have processes that
experience these faults in sandboxes recover, but currently (almost) all
simply terminate the process.  (The divide-by-zero test isn't working,
probably because the compiler is too smart.)

Remove toy sandbox behavior from cheritest as we now use libcheri for
actual sandboxing.
Merge branch 'master' of https://github.com/CTSRD-CHERI/cheribsd