run_dbtest is failing in BF-32465 due to trying to search the bazel sandbox directory, which has directories that are not readable.

The logic in the resmoke wrapper that searches for coredumps is trying to ignore permission errors by piping errors to devnull, but this still triggers a nonzero returncode, failing the script since set -o errexit is on.

Turn off errexit before coredump search and re-enable it afterwards.