Give socket_allow_hosts the ability to handle AF_UNIX sockets

[NSchrading]

Fixes #70

socket_allow_hosts now allows any AF_UNIX socket connection if --allow-unix-socket is specified on the CLI or if allow_unix_socket is used as a pytest mark. It also works for AF_UNIX sockets with known socket (file) names if you pass the correct name in --allow-hosts.

[codeclimate[bot]]

Code Climate has analyzed commit 7f7474d6 and detected 1 issue on this pull request.

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[miketheman]

@NSchrading It's taken me a while to circle back to this, but the internals have been overhauled a fair amount, and many of the behaviors expressed in this PR now work. The named socket and marker are not yet included, so if that's a feature you're really want to see, please reapply the desired behavior on the current code, as now there's conflicts.

[miketheman]

Closing due to lack of response.