Parameterize the base image for the staging image

[jimmykarily]

by extracting bash functions in a sourceable file and using a build arg for the base image.

Also remove unused stack ARG from Dockerfile.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/165491771

The labels on this github issue will be updated when the story is started.

[cfdreddbot]

:white_check_mark: Hey jimmykarily! The commit authors and yourself have already signed the CLA.

[jimmykarily]

This change allows us to build a staging image based on a different stack.

[nimakaviani]

@jimmykarily the staging process is updated/changed significantly and now lives in a separate repo here: https://github.com/cloudfoundry-incubator/eirini-staging/

Also, we are no longer building the binaries for builder and launcher in eirini and strictly rely on the binaries shipped in packs/cf. The longer term plan is to have the code for builder and launcher included in staging and remove the dependency to packs/cf.

In the interim, if you want to change the staging stack, you will need to do a deeper surgical change here: https://github.com/eirini-forks/packs and then create your staging images here: https://github.com/cloudfoundry-incubator/eirini-staging/blob/master/scripts/image.sh

/cc @mattysweeps

[thardeck]

@nimakaviani Thanks for the explanation. Is the old image still being used or was this change already released?

[nimakaviani]

@thardeck the change has not been released yet but we are pulling it into our develop branch. You can track the changes I discussed above in PR https://github.com/cloudfoundry-incubator/eirini/pull/50

The old image is still used in the latest release of eirini if you use native staging.

[jimmykarily]

ok we will look into the new repo first and come back with whatever changes are needed. Thanks. Closing this one.