(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.)
Given that `ssl-exception-thrown?` will either yield a value of `true` or throw an exception, could the use of `true?` be removed from this test and the others below?