(TK-23) Update to clj-http-client 0.2.1

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.)

Conflicts:
	test/clj/puppetlabs/trapperkeeper/services/webserver/jetty9_service_proxy_test.clj
(TK-23) Get rid of unnecessary calls to `true?`