'--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.
We will remove related code in the future.
Support '--suppress-repeated-stacktrace false' to disable suppress mode
Merge pull request #446 from fluent/suppress-repeated-stacktrace-by-default

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