ansible: jenkins: use default-jre-headless

Use default-jre-headless instead of giving the openjdk version, so we
don't need to adjust it to whatever the current version in debian is.

The default-jre-headless package is at least available since debian 10:
https://packages.debian.org/search?suite=buster&arch=any&searchon=names&keywords=default-jre-headless

Related: OS#6186
Change-Id: I6c5c74ff3d75dca2f89765d95c4b4c6d67ace703
1 file changed