Use the Priority Sorter Plugin to make for a smoother first startup

[martindholmes]

When a new TEI Jenkins container is launched for the first time, the order in which jobs are executed is essentially random. This means that some jobs which depend upon prior successful completion of others (such as any of the P5 jobs, which depend upon a successful build of the Stylesheets) may fail, and only later succeed when the prior requirement has been met.

This could be tackled by installing a configured version of this plugin:

https://wiki.jenkins-ci.org/display/JENKINS/Priority+Sorter+Plugin

which is probably not a bad thing to have installed anyway, for managing builds during periods of intensive work. Suggested approach:

Install, configure and debug the plugin on one of the live TEI Jenkins boxes, then take that configuration and (assuming it's in the form of a portable file) add it to this repo. Then add the plugin and its dependencies (if needed -- they all look to be optional) to the build process in the Dockerfile.