SetUp and TearDown at Thead group level

**harsh** ([Bug 60104](https://bz.apache.org/bugzilla//show_bug.cgi?id=60104&redirect=false)):
Hi,

Currently,Tear down and set-up is executed at pre and post execution of all thread group. The purpose of thread group is to set-up or clear the resources.

In load testing or functional testing, set-up or clear the resources also required at thread group level.

this can be done through a sampler, But in this case, many problems occurred.
1) For clean-up purpose, I have to continue test plan even if it fails.
2) By looking at test, I can not say that which are my test step and which are my clean-up and set-up steps.

OS: Linux