spindle: move the clone step out of nixery into a shared package for all spindle engines #827

thanks for the contribution! couple of nits:

• we already have a top level workflow package that also defines CloneOpts (to unmarshal the workflow yaml file however), it is a bit confusing to introduce another workflow package inside spindle with a similar struct CloneOptions (it also shares some of the same fields)
• IMO a simpler route here would be to have a generic CloneStep method that is calculated from tangled.Pipeline_Workflow and returns a struct that follows the models.Step interface

@oppi.li What package would you want this generic cloneStep in?

I think your solution is better, there was no precedent for a custom models.Step outside of nixery, so I was originally trying to avoid that.

I would still eventually want RepoURL and CommitSHA exposed for my usecase. but I might have to just submit a different PR for system-level env vars.

Not entirely sure why this says there are merge conflicts when i rebased master This is an attempt to go off of your design with returning a whole step struct. I think it turns out essentially the same code... so maybe i'm missing something obvious.

that is a bit strange, i don't see anything off with the logs on the knotserver itself. that aside, some comments on the code itself:

• don't think we need to cd workspaceDir, we already have this upon contrainer creation (the WorkingDir is set):

	resp, err := e.docker.ContainerCreate(ctx, &container.Config{
		Image:      addl.image,
		Cmd:        []string{"cat"},
		OpenStdin:  true, // so cat stays alive :3
		Tty:        false,
		Hostname:   "spindle",
		WorkingDir: workspaceDir,

• the rest of the clone code itself looks good to me!
• could you squash the two commits into one? the commit message could be spindle: introduce common clone step or similar

Gave it a once-over; looks good! And thanks for the tests.