Support of img.xz images on JetKVM storage mount

[authrequest]

Adding support for img.xz images created by mrouillard.
Modified usb_mass_storage.go to enable .xz images functionality utilizing "github.com/ulikunitz/xz"

[CLAassistant]

All committers have signed the CLA.

[tutman96]

This will cause a single image to use at least 2x the emmc space to decompress it and store it when mounted. There is a partial implementation of a FUSE (userspace file system) that would enable decompressing on the fly which I think would be better suited for this device? Thoughts?

Optionally maybe it makes sense to decompress it once it is uploaded such that the compressed version isn't stored any more.

[duplexsystem]

There is a partial implementation of a FUSE (userspace file system) that would enable decompressing on the fly which I think would be better suited for this device? Thoughts?

I think this is a better solution, there are three places compression helps:

• Ease of use: Being able to upload compressed images downloaded from distributions without having to decompress them
• Speed of image upload: Self explanatory. This is the least important one.
• Storage space used: Self explanatory. Very important as the storage space on the JetKVM is relatively small and non upgrade-able.

A FUSE library that could support transparent file access of types like .xz, and .bz2 seems like the best solution here.