JettyTester - support for testing redirects

[Andrus Adamchik]

Let's add support for testing HTTP redirects. For this we need an extra "assert" method in JettyTester, and the ability to create WebTargets that do not follow redirects:

WebTarget client = jetty.getTarget(false);
Response r = client.request().get();
JettyTester.assertTempRedirect(r).assertHeader("Location", "/someurl")