Support buildpack feature

[hamakn]

All Cloud Foundry staging process now use buildpack. 👍

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)

[jbayer]

We're not ready to accept this pull request at this time due to reasons explained here https://docs.google.com/document/d/1QEwiHX2tkCVy6LN8V2HMT4qSzoAYR3KeXFm3BbuVE2k/edit?usp=sharing about the focus on getting v2 stable and available. We should be able to revisit this in a month or two. Thank you for your contribution and your patience.

[jbayer]

For the time-being we're going to close this pull request. As mentioned previously, we will be able to revisit backporting buildpacks to v1 once we have the next release publicly available, which should be within several months. Please watch the mailing lists for news. Thanks for your understanding and your contribution.