It looks like this version disappeared from the downloads page within
the past few weeks. I successfully ran this play less than a month ago,
but it started failing a week or two ago, due to the 404 upon download.

I'm admittedly a bit confused as to why there appears to be at least 3
different minor versions of jenkins in use [1][2][3] (plus a major bump
on the build server?! [4]), so I simply cribbed the version used by the
`tools_jenkins` role.

References:
- [1] jenkins_version: "1.638"
- [2] jenkins_tools_version: "1.651.3"
- [3] jenkins_admin_version: "1.658"
- [4] build_jenkins_version: jenkins_2.60.3