[JENKINS-15207] Fix typo in warning message when config-file-provider pl...
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fixing NPE introduced by change offline note feature
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no need to call toString() on the string
add comments

 - massaging exception handling
 - leaving a TODO for a possible future enhancement

@kohsuke suggests using '@' as separator between shortName & version, rather than ' ', in case we want to allow multiple owners in the future.

[FIXED JENKINS-14667] JDK installation failed on some slaves with InvalidClassException: hudson.tools.JDKInstaller$Platform$1; local class incompatible: …

return a string literal vs a new string object
switching to implicit else

(cherry picked from commit 43ff1688)

From what I was told by Emanuele today in the office hours, this came up
during the Copenhagen hackathon.

Put slave back online automatically, if there's enough disk space again ...

Javadoc improvements inspired by “How to stop passwords used by my scm plugin from appearing the log?” on jenkinsci-dev.

Added callable wrapper to actAsync