Add jenkins as host alias to jumpbox-1

So that scripts (ie sensu alerts) can access Jenkins to eg download
build artifacts.

Related to https://www.pivotaltracker.com/story/show/67409248

[#67409248]
Merge pull request #385 from alphagov/add-jenkins-to-hosts

Add jenkins as host alias to jumpbox-1
Sensu check script for pp-smokey output

This script is run with a pp-smokey test name, ie `backdrop_read`. It
downloads the latest pp-smokey results from Jenkins and parses the
output. It returns an exit code which a Sensu check can interpret (ie 0
is OK, 3 is CRITICAL)
Add sensu::checks for each pp-smokey feature

These run on the monitoring box invoke the smoke test checker script
every minute.

https://www.pivotaltracker.com/story/show/67409248

[Delivers #67409248]