Create build

[sdomino]

A build represents a "Packer run"; the point of a build is the ability to post a build with all necessary information that a Packer run will need, at which point the client disconnects to follow up with the progress of the run.

When a build is posted, validation is needed to ensure that the template being used actually exists in the DB.

builds:
id - UUID generated on create
template_id - ID of base template
state - incomplete, complete, failed
status - installing template, copying template, transforming template, running packer, recording results, cleaning up
last_updated -
transform_payload - payload that will get passed into the transform_script from template
meta_data - return data from [Packer]

build_logs:
id -
build_id -
message -
created_at -

Build process:

1. Create entry in DB that represents the build
   1.5 At a short interval, update last_updated field (goroutine) because packer run might take time
2. Install template on local node if not already available ([/var/db/sherpa]/templates/:id)
3. Copy template into a tmp build folder for duration of build ([/var/db/sherpa]/builds/:build_id)
4. Run transform script (builds/:build_id/{{transform_script}}) if present, passing transform_payload
5. Packer run (all output (\n) is a new build_log for that build); update last_updated/state of build throughout process
6. Record - take packer info and dump it into meta_data
7. Cleanup - delete build folder