Allow published repo to reside on different filesystem

[l1k]

Requirements

All new code should be covered with tests, documentation should be updated. CI should pass.

Description of the Change

Currently packages are hardlinked from the internal pool to the published repo, which requires them to reside on the same filesystem. This precludes mounting the published repo from a remote machine, e.g. via NFS or sshfs, which would be desirable to physically separate the machine hosting the internal pool and signing key from the machine serving the published repo.

Autodetect such a setup and, if found, copy files instead of using hardlinks.

Add helpers to check whether two given paths reside on the same filesystem and to check whether an already published package file is identical to the one to be published by comparing their MD5 hashes.

Checklist

• unit-test added (if change is algorithm)
• functional test added/updated (if change is functional)
• man page updated (if applicable)
• bash completion updated (if applicable)
• documentation updated
• author name in AUTHORS

[smira]

Thanks for the contribution, it seems to be somewhat close to #519, I thought if we could do the same trick here by opening up local filesystem publish roots?

I can work on the PR to provide that, and we can add option to copy files/symlink them after that?

[l1k]

Okay, I'll wait for @seeraven to update his pull, then rebase. Or perhaps his pull will already include the copy functionality.

@seeraven feel free to ping me if you need help/testing/reviewing.

Meanwhile, I've rebased on current master and all tests fail because of a golint warning which is a false positive: "hardlinked" is a misspelling of "hardline" (misspell) Perhaps misspellings can be demoted from hard errors to noncritical warnings? Thanks!

[seeraven]

I've just created a new pull request https://github.com/smira/aptly/pull/521 with a new approach to specify one or multiple local endpoints with a customizable link method (hardlink, symlink or copy). Let me know if this works for you.

[l1k]

Closing in favor of #521.