HTTP Request: Migrate to HTTPClient 5 APIs

[asfimport]

@pmouawad (Bug 63456): Hello,

This could be a good start for future HTTP2 support.

Regards

OS: All

[asfimport]

Michael Osipov (migrated from Bugzilla): You should continue to support both HttpClient4 and 5. Many many software will remain on 4 for a long time.

[DidierLoiseau]

Now that JMeter actually depends on HttpClient5 (see #5936), it would probably make even more sense.

This seems indeed to be a prerequisite for HTTP/2 (#4023)