ci: Add build with Java 7 on Linux
ci: Add build with Java 7 on Linux

Add a job to run a build with Java 7.
The job currently only runs on Linux.
In order to run on Java 7, an old Ant version is downloaded and
installed. We use moxie+ant for this, so we build with moxie.

gitblit/gitblit,fzs/gitblit,fzs/gitblit,fzs/gitblit,fzs/gitblit,gitblit/gitblit,gitblit/gitblit,gitblit/gitblit,gitblit/gitblit,fzs/gitblit