Add nomad driver for Facebook eXecutable ARchives (XAR)

[sboisson]

Facebook has developed and deployed XARs, or eXecutable ARchives, a system for distributing self-contained executables that encapsulate both data and code dependencies.

https://code.fb.com/data-infrastructure/xars-a-more-efficient-open-source-system-for-self-contained-executables/

A XAR is a simple combination of a few primitives:

• A four-kilobyte preamble that is a shebang pointing to a helper executable (#!/usr/bin/env xarexec_fuse)
• A helper, xarexec_fuse, that knows how to read the XAR file, mount it if necessary, and execute the Python (or Lua or …) script inside
• A FUSE filesystem, squashfuse_ll, that is responsible for making the squashfs file look like a normal directory of files (and, by using FUSE, XARs don’t require root to run and can run on OS X).
• (optional) Since squashfs supports Zstandard compression (another Facebook open source offering), we can achieve far better compression ratios and faster decompression speed than zlib-based zip files can.

https://github.com/facebookincubator/xar

[chelseakomlo]

Thanks for opening this request- Nomad 0.9 will add support for pluggable externally-maintained drivers, so this is something that can be externally written and used by the community in later Nomad releases.

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