Fix printing exception message

[hawflau]

Which issue(s) does this change fix?

N/A

Why is this change necessary?

To match previous behavior in terms of printing unhandled exception

How does it address the issue?

print str(ex) instead of repr(ex)

What side effects does this change have?

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.