(TK-23) Update to clj-http-client 0.2.0

This commit updates jetty9 to the latest clj-http-client release,
and in the process, fixes some transient test failures having
to do with a race condition.  (SSL-related tests that were intended
to cause exceptions could end up with one of two different exceptions
when we use an asynchronous HTTP client.)
I've found in the past that putting the assertions inside a function or macro seems to make it *less* clear which test caused the failure; at least, when running from a REPL.

I'd be open to adding more description to the assertions that are calling the macro, but I personally don't think it adds enough value to warrant spending more time on it right now.  If you disagree then I can go back in and add some stuff.