Prevent git hardlinks when cloning locally
Prevent git hardlinks when cloning locally

When a ReviewBot RepositoryTool clones, it runs `git clone` with the `--local`
flag, which among other things, saves space by using hardlinks. Since
`repository.py` attempts to clone into `/tmp`, which is often a ramdisk, it's
considered a separate device. Hardlinks don't support this, so the tool fails
to run with:

    `fatal: failed to create link <path> Invalid cross-device link`

This patch adds `--no-hardlinks` to the clone which allows us to still use
`/tmp`, but it doesn't fail on local repositories.

Testing Done:
I've tested this by adding a new review request after patching which correctly
clones and runs my own reviewbot plugin.

Reviewed at https://reviews.reviewboard.org/r/10172/

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