Also use cache dir as temporary directory, solving cross-disk copy errors

[inteon]

Prevent the following error from occurring: panic: failed to fetch targets: rename /tmp/klone-1469327034/modules/boilerplate /home/username/.cache/klone/47952611b91a53de34be5ba9fba781: invalid cross-device link

[ThatsMrTalbot]

I think this would still panic if the home directory was on a different filesystem to the working directory, since rename does not perform a file copy like cp.

[ThatsMrTalbot]

It looked like dep had a function similar to what we want, it attempts a os.Rename, but falls back to doing a copy
https://github.com/golang/dep/blob/v0.5.4/internal/fs/fs.go#L159

[inteon]

@ThatsMrTalbot
The temporary folder is moved to the cache folder:

klone/pkg/cache/clone.go

Lines 70 to 72 in e2d88b8

	if err := os.Rename(outPath, cachePath); err != nil {
	return err
	}

The cache folder is copied into the project:

klone/pkg/cache/clone.go

Lines 88 to 90 in e2d88b8

	if err := cp.Copy(cachePath, destPath); err != nil {
	return err
	}

So, the only move we do is from temp to cache, which is what this PR changes.

[ThatsMrTalbot]

Ah, ok. I saw the os.Rename at the bottom and it read like the cache was being copied to the destination

/lgtm

[cert-manager-prow]

@ThatsMrTalbot: adding LGTM is restricted to approvers and reviewers in OWNERS files.

In response to this:

Ah, ok. I saw the os.Rename at the bottom and it read like the cache was being copied to the destination

/lgtm

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[inteon]

/approve

[cert-manager-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: inteon

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[ThatsMrTalbot]

/lgtm