nixos: Create persistent storage directories and their parents

[talyz]

If they're not filesystem roots, they won't exist when deploying to a new system and would otherwise have to be manually created.

Fix #154

cc @tmarkov

[tmarkov]

I'll try to try this tomorrow. Out of curiosity, why isn't simply passing -p to mkdir good enough?

[talyz]

It opens up for directories being created with the wrong permissions and ownership if they're created in the wrong order. You would always have to consider the possible side effects of it, basically. Explicitly creating all directories in the hierarchy gives much better control and makes potential issues easier to pinpoint.

[visualphoenix]

any reason why this removes quoting in the bash part?

[tmarkov]

Sorry for the delay, had trouble setting up a test vm properly.

But everything seems to work fine (at least on my config).