Add a way to clear a Cookie on demand

@pmouawad ([Bug 53976](https://bz.apache.org/bugzilla//show_bug.cgi?id=53976&redirect=false)):
The aim is to clean a Cookie with more flexibility than today.

See:

- http://stackoverflow.com/questions/12707635/how-to-clear-jsessionid-of-each-threaduser-in-jmeter-on-demand

- http://stackoverflow.com/questions/12670264/simulating-interaction-between-two-users-in-jmeter

Votes in Bugzilla: 1
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