Support buildpack feature

All Cloud Foundry staging process now use buildpack. :+1:

CCng is nice, but I'm still using CCv1 for some reasons,
so I implement buildpack feature in CCv1.

This patch does not to disturb any existing features on CCv1.
I checked this patch send a buildpack url to DEAng or deprecated Stager and they start to clone the buildpack.

To use this patch, you need to
- patch vmc https://github.com/hamakn/vmc/tree/buildpack_for_v1 and vmc-lib https://github.com/hamakn/vmc-lib/tree/buildpack_for_v1
- deploy manifest file for buildpack like this 
https://github.com/hamakn/cloud_controller/blob/buildpack/cloud_controller/spec/support/manifests/buildpack.yml
to AppConfig[:directories][:staging_manifests] directory (using dev_setup or cf-release)