[FIX JENKINS-33127] BootFailures send HTTP 500

Remove broken XStream2 test of legacy custom ConcurrentHashMapSerialization

[FIXED JENKINS-33319] Premtively wake the acceptor thread to let it close cleanly

Excluded jenkins-war from the test harness.

Latest & greatest version of Stapler

Previously, when the 2nd `e.click()` is called, the page has already transitioned to another page, so the anchor objects have become invalid.

HtmlUnit somehow still manages to follow a link, except when there's some JavaScript attached to the onclick() handler it's going to execute in a strange environment. Some management link requires a POST, and that was done via JavaScript. So that broke the test.

Whilst this is not used in the dependencies, the enforcer plugin downloads
the i1.580.1 jar so it can scan it.  Most likely a bug in the
extra-enforcer-rules but we obviously don;t need it as we have an explicit
dependency on the latest version!

[FIX JENKINS-32303] Fix readonly behavior for f:checkbox

- Also adds a Ping Agent protocol that could be used by nagios monitoring, etc. to verify that the slave agent listener is alive
- We use the ping agent protocol to ensure that the acceptor thread wakes up, loops and sees that the shutdown is started
  that prevents the socket close exception from being thrown

Remove the broken ConcurrentHashMapConverter impl, since it handles a conversion dating back to 2010 and does not work with Java 8

This one requires some explanation: there is a bug
As custom serialization of ConcurrentHashMaps was removed circa 2010
(see eb51d46d)

We can assume that testing conversion is no longer a high priority.
Root cause appears to be a subtle change in the XStream attribute access behavior when run under JDK8 only.
This appears to be the only case that triggers it.

Integrate newer version of test-harness

Removes mention of http.proxyHost property

The root problem was missing <scope>test</scope> in domain-discovery.

[JENKINS-33068] AsyncPeriodicWork/AsyncAperiodicWork log files rotation

Fix proxy server name documentation

Pull in new version of Stapler