JJB runner POC

The initial work to support running job instructions pulled in from
jenkins-job-builder config.

Because the XML is tightly coupled with JJB it's easier to use
xmltodict at this point. Ideally a new interpreter for JJB formatted
files to turbo-hipster instructions could be made.

At the moment we're ignoring JJB instructions from items we aren't
interested in (for example, publishers and build wrappers). Some
level of support should be added later for these or the job
instructions should be updated to not use them.

Change-Id: I0560d8e0a7e33548bacee3aa98bd45a5907bec21