Add scap/scap trebuchet target

Step one in a two step process to convert the delivery of the scap
scripts themselves from a puppet managed git clone to a project deployed
by trebuchet.

When we originally split the scap scripts out as a separate project from
operations/puppet it was configured to be deployed using git::clone.
This has mostly worked out well, but there have been a few
complications. We have had file permissions issues on more than one
occasion with the git clone. It also means that code changes start
appearing on the cluster as soon as gerrit merges them into the master
branch.

Now that scap is being used to deploy MediaWiki in the beta environment
it would be nice to have the ability to update code there for testing
separately from the production cluster. Although there are many means to
accomplish this goal it seems that using trebuchet is the easiest to
enable. This will also be good dog fooding for the likely eventuality of
scap merging into or at least partnering with trebuchet to perform
MediaWiki deployments.

Change-Id: I3c9ba6bd86aa582a75f61d317091594033409777