Adjust tests for final version of shtk_abort
Adjust tests for final version of shtk_abort

The draft implementation of shtk_abort signaled the calling script but the
final version just exits cleanly.  Fix tests to cope with this new behavior.

Additionally, shtk_abort may now also create a helper script under certain
conditions, which is removed on exit using rm, so we cannot track whether
rm has been called for sanity purposes.  Just rely on the chmod tracking
that we already had.

jmmv/sandboxctl