Bump min version of Jenkins to 2.204.4

[pjdarton]

We currently have a failing unit test in #835 that does not appear to be related to that PR.
What we're seeing is that the DockerNodeStepTest unit test is failing with exception:

WARNING	h.m.DownloadService$Downloadable#updateNow: signature check failed for http://localhost:37881/updates/hudson.tasks.Maven.MavenInstaller.json
ERROR: Signature verification failed in downloadable 'hudson.tasks.Maven.MavenInstaller' java.security.SignatureException: Signature length not correct: got 512 but was expecting 256
	at sun.security.rsa.RSASignature.engineVerify(RSASignature.java:189)
	at java.security.Signature$Delegate.engineVerify(Signature.java:1222)
	at java.security.Signature.verify(Signature.java:655)
	at sun.security.x509.X509CertImpl.verify(X509CertImpl.java:444)
	at sun.security.provider.certpath.BasicChecker.verifySignature(BasicChecker.java:166)
	at sun.security.provider.certpath.BasicChecker.check(BasicChecker.java:147)
	at sun.security.provider.certpath.PKIXMasterCertPathValidator.validate(PKIXMasterCertPathValidator.java:125)
Caused: java.security.cert.CertPathValidatorException: signature check failed
	at sun.security.provider.certpath.PKIXMasterCertPathValidator.validate(PKIXMasterCertPathValidator.java:135)
	at sun.security.provider.certpath.PKIXCertPathValidator.validate(PKIXCertPathValidator.java:233)
	at sun.security.provider.certpath.PKIXCertPathValidator.validate(PKIXCertPathValidator.java:141)
	at sun.security.provider.certpath.PKIXCertPathValidator.engineValidate(PKIXCertPathValidator.java:80)
	at java.security.cert.CertPathValidator.validate(CertPathValidator.java:292)
	at org.jvnet.hudson.crypto.CertificateUtil.validatePath(CertificateUtil.java:93)
	at jenkins.util.JSONSignatureValidator.verifySignature(JSONSignatureValidator.java:78)
	at hudson.model.DownloadService$Downloadable.updateNow(DownloadService.java:416)
	at io.jenkins.docker.pipeline.DockerNodeStepTest$3.runTest(DockerNodeStepTest.java:237)
	at io.jenkins.docker.pipeline.DockerNodeStepTest$3.evaluate(DockerNodeStepTest.java:228)
	at org.jvnet.hudson.test.RestartableJenkinsRule$6.evaluate(RestartableJenkinsRule.java:272)
	at org.jvnet.hudson.test.JenkinsRule$1.evaluate(JenkinsRule.java:596)
	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:298)
	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:292)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.lang.Thread.run(Thread.java:748)

This may be related to JENKINS-31089 and that said it was fixed in later versions of Jenkins, so this PR fixes this issue by updating our "minimum" version of Jenkins to the oldest officially supported (2.204.4 according to this page at the time this was written) ... and doing that seems to work...

However, the docker-plugin's dependencies have, traditionally, been largely left unloved and unmaintained.
This test failure seems to be the point where we've hit a breaking point and to fix this has (I think) necessitated a dependency move forwards, and the best way of doing that is to also move the way these dependencies are handled "forwards" too.

What this PR is attempting to do is to bump the minimum version of Jenkins to the oldest officially supported (2.204.4) and then to use the Jenkins "BOM" plugin to then figure out what version of everything else that we use needs to be (in order to avoid the dreaded "upper bounds" maven error).
This has required numerous changes to the pom.xml file that really need reveiwing by someone who understands this better than I do.
(There's also a few changes elsewhere in the code as a result of dependencies changing to non-ancient versions, but they're trivial by comparison.)

[pjdarton]

HELP WANTED

The docker-plugin's dependencies have, traditionally, been largely left unloved and unmaintained.
I'm the current custodian of this plugin and I do not have a great understanding of maven dependencies, or how Jenkins dependencies are done using maven.
I would really appeciate someone who does understand dependencies reviewing the changes I'm making to the pom.xml file here.

@rdica @andrei-barna @Osipion @bguerin - you've all got PRs and/or defects you're interested in seeing merged so I figure that I'll ask you all first ... and if you don't know this subject any better than I do but you know someone who does, please do point them in this direction.

[bguerin]

Hello !
To get confident with these changes, the first thing to do is running mvn help:effective-pom before your changes and then again after your changes. You will obtain the full POM, completly expanded, the diff is here :
diff_effective_pom.txt

First changes, in the dependencyManagement section are just about versions of the dependencies that the plugin could use. They are really used if declared in the dependencies section. Both theses changes seems good to me.
There are also changes in the plugins section, mostly version upgrades. Also fine to me, means plugin will use more recent plugins, with bug fixes.

Second thing to do it to list the dependencies tree (again, before and after), mvn dependency:tree. Here is the diff :
diff_dependency_tree.txt

Looking only at the first level (.*[INFO] +-.*), these seems coherent with what you want to do.

If you want, I can test your branch on my installation : up-to-date jenkins and pipeline plugins, running in docker, building through docker agent, JNLP connected.

If I could, I would approve this, and thanks for your work !

[pjdarton]

Thank you for the (excellent) explanation and detailed investigation; that is exactly what I was hoping for.

Yes, if you can test it then please do so. I'll see if I can find a few Jenkins servers to put it on at work tomorrow too.
If it all goes well, I'll press the merge button ... and hopefully that'll then lead to other PR builds passing, and make life easier for all...

Once again: thank you for your analysis - it's much appreciated.

[bguerin]

Welcome ;)

Building your branch and upgrading the plugin on my installation. Keep you posted

[bguerin]

Changes successfully tested on my installation

[pjdarton]

My own testing suggests that it's harmless too - I'll merge it...