Get test running scripts to detect and report common error.

testing/tools/run_corpus_tests.py assumes a debug build and will
fail cryptically if only a release build is available.

Arguably there shouldn't be a default because having one could lead
to accidentally running a stale version, but that is probably too
much of a change.

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1150823003
3 files changed