(Bug #22166) rm hardcoded hostname dependencies

Prior to this, we had hardcoded burji.puppetlabs.com into
build_defaults.yaml. Since this isn't particularly elegant, this commit
takes that out, and instead uses cnames that point to the right place,
be it burji, or something newer (like burji2)
Merge pull request #143 from melissaanne/maint/stable/rm-hardcoded-dependencies

(Bug #22166) rm hardcoded hostname dependencies