- A pure unit tests will suffice

- Also fixes to append `&uctest` if the update center URL already contains a query fragment

[JENKINS-36717] - FindBugs cleanup

'{0}' is the literal string {0} in a message format - if you want to quote
the parameter then you need to use double single quotes ''{0}''

Fixed issues:
* [JENKINS-37140](https://issues.jenkins-ci.org/browse/JENKINS-37140) -
JNLP Slave connection issue with *JNLP3-connect* protocol when the generated encrypted cookie contains a newline symbols.
(https://github.com/jenkinsci/remoting/pull/95)
* [JENKINS-36991](https://issues.jenkins-ci.org/browse/JENKINS-36991) -
Unable to load class when remote classloader gets interrupted.
(https://github.com/jenkinsci/remoting/pull/94)

Enhancements:
* Improve diagnostics for Jar Cache write errors.
(https://github.com/jenkinsci/remoting/pull/91)

[FIXED JENKINS-37223]

report the server's address, too

Added a simple diagnostic HTTP response to the TcpSlaveAgentListener.

* [FIXED JENKINS-31791] Optimize BuildHistoryWidget

Refactor HistoryPageFilter to lazily evaluate an iterable of previous
runs, instead of instantiating a super long list of builds.
Instantiating the whole list can be problematic with lots of
historical builds especially if disk IO is slow.

FindBugs: get rid of the redundant null check in hudson.model.queue.Executables#getEstimatedDurationFor()

FindBugs: The tool cannot into StringUtils.isBlank(), so we optimize the code to workaround it (not a bug)

FindBugs: Handle the non-realistic case of null Staplerrequest in HudsonPrivateSecurityRealm#newInstance()

FindBugs: Violation of Descriptor newInstance() contract in hudson.scm.RepositoryBrowsers#createInstance deprecated method

FindBugs: Optimize logic of ChannelPinger#pingInterval initialization in order to fix the Integer unboxing issue in the original code

Queue.ItemList: Be sure we cleanup the list instead of the entire Queue (IA_AMBIGUOUS_INVOCATION_OF_INHERITED_OR_OUTER_METHOD)

* Move FindBugs call to the parent POM, always run it and generate XMLs

* Update FindBugs to 3.0.4

* Filter away Stream encoding issues

* Rework FindBugs definitions according to comments from @jtnord

* Generalize configuration, findbugs:findbugs now takes it.

* Add TODOs to FindBugs excludes file

* Remove explicit failOnError

* Fix the typo spotted by @jtnord