Jenkins.getComputers may be called frequently; do not perform an expensive locale-sensitive sort each time.

(Also relevant to JENKINS-22395 diagnostics.)

Start cron at zero seconds after the minute, and ensure the internal calendar is set to zero seconds.  Allows for more predictable behavior.

[FIXED JENKINS-22672] Make /threadDump easier to use.

[FIXED JENKINS-22688] Made graph font explicit and configurable

[FIXED JENKINS-22689] Show load statistics for master node

Instead, use a distance of 0.5x the width/height of the label.

This improves appearance in combination with JENKINS-22688 for
different font sizes.

Debian postinst: check for present user/group before adding them