(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 think the extra detail is useful but won't ask that we hold up this PR to get it in.  If we find that we're getting more intermittent fails after the changes go in, we can revisit doing something more in the tests to get the extra detail we'd need to troubleshoot these further.