* Do not load detached plugins during tests.
Also warn about plugins which force us to create classes.jar.

* Porting POM fix from #2795: we must allow snapshots from repo.jenkins-ci.org so as to be able to test upstream component PRs.

* Fixed failures in tests which assumed detached plugins were being loaded.

* jenkins-test-harness 2.20

* Unreproducible test failure on CI, probably due to timing.

(cherry picked from commit 72901698)

Use rerunFailingTestsCount rather than @RandomlyFails
(cherry picked from commit c54c363b)

Obsolete with Java 8. Permanent generation was removed.

[FIXED JENKINS-33595] Picks up https://github.com/jenkinsci/sshd-module/pull/11
to turn off SSHD by default, but expose it to tests which wish to enable it.