make HTTP sampler to check certificate on SSL/TLS connections

**ateles.belzebuth.hybridus+apache** ([Bug 57717](https://bz.apache.org/bugzilla//show_bug.cgi?id=57717&redirect=false)):
The HTTP Sampler does not check the server certificate during the TLS handshake. This behavior opens the connection to man-in-the-middle attacks. While this behavior is acceptable for test scenarios where security is not a concern, it can become a serious problem in a productive environment; e.g. if JMeter is used for performance monitoring of a web application.
Can you add a switch (checkbox or jmeter property) that allows enabling certificate checks?

Best regards, @

OS: All