Make copy_reference_file quieter

[jglick]

Produces way too much output if you have a lot of files in /usr/share/jenkins/ref. @reviewbybees

[ndeloof]

but this is useful to diagnose bootstrap issues. Could maybe support some -q flag (or add -verbose) to disable output

[jglick]

I think it should be quiet by default. If you need to diagnose anything, these messages could be written to a log file inside the container.

[ndeloof]

docker practice is to send logs to stdout, so that docker log can collect them. Don't use log files inside container

[jglick]

Well it is just too much noise for something you do not normally want to look at, when as a user you are interested in the Jenkins log, not some file copying inside the container. It is only because of the VOLUME trick that this copying even happens at runtime; normally this sort of thing would be part of docker-build.

[ndeloof]

sure, but jenkins design to merge config and plugin files in jenkins_home doens't help :-P
At least, such a log file should live in /var/log to follow linux conventions

[jenkinsadmin]

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