adding -e flag to not delete the bucket but just empty it

[CpuID]

I have a scenario where doing some large scale testing, we want to empty the bucket after each attempt basically. Deleting the bucket doesn't work so well as theres a blackout period where you can't reuse the same bucket name for a short period thereafter (15~mins or so). Just emptying it was our preference, added a flag for it, current defaults are unchanged.