Note what to do to build vagrant box

[Closes #13]
clone custom buildpacks outside of app dir

some buildpacks (e.g. php) move everything in the app dir elsewhere, and
blow up in weird ways

[finishes #43361489]
Fix integration spec

After buildpacks get cloned outside app dir,
the size of droplet is decreased.
Dea publishes droplet exit status, description during crash.
Set exit status and exit description before state change.