Ensure bootstrap.sh can write to overlay fs

[agraul]

What does this PR change?

We can't assume that the overlay dir corresponding to the transaction we open contains the minion config directory. For example, when venv-salt-minion was previously installed and bootstrap.sh is executed again, the new overlay dir might not have etc/venv-salt-minion.

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No difference.

• DONE

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• DONE

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• DONE

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[agraul]

Changelog test stumbles over a period that's not separating two sentences 🤷‍♂️

[m-czernek]

I'm not sure I understand here, but if the only problem is that we could re-execute the bootstrap script multiple times, shouldn't we just continue in the previous transaction?

In new_transaction, we use /usr/sbin/tukit -q open, we could use /usr/sbin/tukit --continue --discard -q open instead?

[agraul]

There might have been transactions in between the one that added etc/venv-salt-minion/ and the latest. I didn't want to search all the transactions, thought it was cleaner to "onboard in a new transaction", no matter what happened before.

[m-czernek]

Hmm, that sounds about right. I suppose this would be situational. Perhaps at some point we could let the users decide whether they want a new transaction or continue in previous one.