fix(slugbuilder): allow users to cat slugfile

partially reverts deis/slugbuilder@b872515
style(builder): convert tabs to spaces
chore(contrib/rackspace): bump to CoreOS 494.5.0
Merge pull request #2808 from carmstrong/rackspace-494.5.0

chore(contrib/rackspace): bump to CoreOS 494.5.0
Merge pull request #2794 from bacongobbler/2740-slugbuilder-to-stdout

fix(builder): allow users to cat slugfile