[FIXED JENKINS-21999] If a slave node does not exist it will throw a
null pointer exception. Instead we create a dummy launcher and return
that if it is unable to get the slave node.
Throw IOException if trying to launch a DummyLauncher. Restrict
DummyLauncher class to no external use.
improve a bit previous commit
Merge branch 'JENKINS-21999' of github.com:christ66/jenkins
[JENKINS-21999] Noting merge of #1145.
OldDataMonitorTest.robustness consistently passes for me locally, but has been causing trouble in CI. Suppressing for now.
fix test due to jglick comment
add logging if file does not exist
[JENKINS-22354]

Avoid having FilePath to depend on Jenkins, which increases the amount of classloading that has to happen during remoting
[JENKINS-22354]

Reduce classloader activities.

This brings in Stapler and commons bean-utils that we don't need on the
slaves.
fixed a test regression
Add missing at-since
Merge pull request #1174 from daniel-beck/at-since

Add missing at-since
need to handle half-close correctly
typo
Merge pull request #1173 from olamy/not-try-to-load-non-existing-files-improved

improve a bit previous commit
[maven-release-plugin] prepare release jenkins-1.558
[maven-release-plugin] prepare for next development iteration
updated changelog for release
updated changelog as a part of the release