CookieManager cleanup in postprocessor behaves strangely

@FSchumacher ([Bug 64145](https://bz.apache.org/bugzilla//show_bug.cgi?id=64145&redirect=false)):
Mail from Philippe on the dev mailing list:

Hello,
I was looking into clearing cookies at some step of my scenario.

So under an HTTP Request I added a JSR PostProcessor , I called:

- sampler.getCookieManager().clear()

But although it clears cookie it seems it breaks further iterations,
Cookies are not added
The workaround is to do this:

- sampler.getCookieManager().testIterationStart(null);

Don't have time to investigate more deeply for now, just reporting not to
forget it.

Severity: normal
OS: All