tests: Fail checkpoint regressions if no cpt has been taken

tests: Fail checkpoint regressions if no cpt has been taken

This is to avoid the scenario where a wrong interval is chosen
and no checkpoint is taken.

Change-Id: I524d797048ab04799555aaf7a051241b2917ad95
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27710
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Gem5 Cloud Project GCB service account <345032938727@cloudbuild.gserviceaccount.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>