Modify Dockerfile layering

[mands]

From @mands on October 12, 2015 17:30

Need better mechanism to build containers and current layering is brittle and doesn't allow for updating lower-level layers with new code (i.e. baseos, lang, stackhut runner) without a full re-deploy.

Currently can't update deps without service redeploy. Need to restructure layering system, should hopefully provide builder speedup due to caching also.

New method handles this is a much better way forcing last-minute linearisation of all dependencies whilst storing the user service artefact for later updates.

Steps -

• Move buildstacks into internal scripts
• Add stack update command to internal scripts
• Change layering system as described above

Copied from original issue: #5