Better exception message if a SecurityRealm doesn't respect the API contract and return null (#2407)

* Getter exception message if the SecurityRealm doesn't respect the API contract and return null.

* Use NullPointerException instead of IllegalStateException to not change the behaviour of the method.

* [JENKINS-33600] - User#isIdOrFullnameAllowed() should be tolerant against null parameters

* [JENKINS-33600] - Add the follow-up TODO

Changes summary:

Fixed issues:
* [JENKINS-22722](https://issues.jenkins-ci.org/browse/JENKINS-22722) - 
Make the channel reader tolerant against Socket timeouts. 
(https://github.com/jenkinsci/remoting/pull/80)
* [JENKINS-32326](https://issues.jenkins-ci.org/browse/JENKINS-32326) - 
Support no_proxy environment variable. 
(https://github.com/jenkinsci/remoting/pull/84)
* [JENKINS-35190](https://issues.jenkins-ci.org/browse/JENKINS-35190)  - 
Do not invoke PingFailureAnalyzer for agent=>master ping failures. 
(https://github.com/jenkinsci/remoting/pull/85)
* [JENKINS-31256](https://issues.jenkins-ci.org/browse/JENKINS-31256) - 
 <code>hudson.Remoting.Engine#waitForServerToBack</code> now uses credentials for connection. 
(https://github.com/jenkinsci/remoting/pull/87)
* [JENKINS-35494](https://issues.jenkins-ci.org/browse/JENKINS-35494) - 
Fix issues in file management in <code>hudson.remoting.Launcher</code> (main executable class). 
(https://github.com/jenkinsci/remoting/pull/88)

Enhancements:
* Ensure a message is logged if remoting fails to override the default <code>ClassFilter</code>. 
(https://github.com/jenkinsci/remoting/pull/80)

[FIXED JENKINS-35641] - Always send usage statistics over HTTPs to the new usage.jenkins.io hostname(#2398)

References INFRA-559

[JENKINS-35098] Disable AutoBrowserHolder by default to improve the changelog rendering performance (#2371)

* [FIXED JENKINS-35098] Deleting AutoBrowserHolder.

* Normalizing form binding scheme for AbstractProject.scm.

* At @oleg-nenashev’s insistence, restoring AutoBrowserHolder, though not using it by default.

* Using SystemProperties at @oleg-nenashev’s recommendation.

[JENKINS-34923]

[JENKINS-34751] updated Groovy to 2.4.7

follow-up for JENKINS-34751

[FIXED JENKINS-35402] Make it easier for update sites to tweak the InstallationJob

Signed-off-by: NNicolas De Loof <nicolas.deloof@gmail.com>

Commit 7efb9090 seems to have done
without paying attention to what javadoc refers to.

Removed code duplication

[FIXED JENKINS-33780] Introduce listener for slave creation/update/deletion

getItem() and contains() act exactly the same

[FIXED JENKINS-31915] Proxy settings in plugins page are ignored