'--suppress-repeated-stacktrace' is true by default

We keep this option for backward compatibility.
Maybe, there is no user who wants to disable this option on production.
We will remove related code in the future.

From this patch, fluentd behaviour is:

1. without '--suppress-repeated-stacktrace', suppress logs
2. with '--suppress-repeated-stacktrace', suppress logs
3. with '--suppress-repeated-stacktrace true', suppress logs
4. with ''--suppress-repeated-stacktrace false', no suppress logs