Fix issue where restart would not properly display username if user was
not loaded.
Revert "Fix issue where restart would not properly display username if user was"

This reverts commit 7dbefd7463a9c580b04ff07d4123a1885a08641d.
UserIdCause.getUserName and UserCause.getUsername should both create a
user if the user does not exist.
Remove unnecessary parameter in method call. Also return "anonymous" if
User is null.
When userId is null then return anonymous, otherwise try to obtain the
display name.
[FIXED JENKINS-20662] Establish relation to new build immediately.
[FIXED JENKINS-22672] Make /threadDump easier to use.
[JENKINS-20662] Add test.
[FIXED JENKINS-22688] Made graph font explicit and configurable
[FIXED JENKINS-22689] Show load statistics for master node
the trunk is toward 1.562-SNAPSHOT
Debian postinst: check for present user/group before adding them

In git commit 7216aab0d the check for present user was removed
and therefore upgrading the Debian package on existing Jenkins
installations fails. Also the newly added code for adding a
configurable Jenkins group is missing a check for a possibly
already present Jenkins group.

Closes: JENKINS-22710
simplify logic to avoid code duplication
Merge pull request #1167 from christ66/ZD-16606

Fix issue where restart would not properly display username if user was not loaded.
Moving the logic into an inner class.

This is in preparation of resolving dependencies within "List<URL> all"
Resolving dependencies among other JPL files
defer MavenEmbedder creation
made this list configurable
a test case that reveals a bug in AtmostOneTaskExecutor
Fixing a bug.

pending was null as soon as task started running, so it was possible that another thread submits the task and have that executed while the first one was still running